v1.0.5

.github/workflows/ci-retry.yml

@@ -0,0 +1,29 @@
+name: "CI retry"
+
+on:
+  workflow_run:
+    workflows: ["CI"]
+    types: [completed]
+
+permissions:
+  actions: write
+
+jobs:
+  rerun:
+    name: Re-run failed jobs
+    if: >
+      github.event.workflow_run.conclusion == 'failure' &&
+      github.event.workflow_run.run_attempt < 3
+    runs-on: ubuntu-latest
+    steps:
+      - name: Re-run failed jobs
+        env:
+          GH_TOKEN: ${{ secrets.CI_RETRY_TOKEN || github.token }}
+          GH_REPO: ${{ github.repository }}
+          RUN_ID: ${{ github.event.workflow_run.id }}
+          RUN_ATTEMPT: ${{ github.event.workflow_run.run_attempt }}
+        run: |
+          set -eu
+          echo "Run $RUN_ID failed on attempt $RUN_ATTEMPT, re-running failed jobs"
+          sleep 60
+          gh run rerun "$RUN_ID" --failed

.github/workflows/ci.yml

@@ -18,6 +18,8 @@ env:
   SCCACHE_GHA_ENABLED: true
   RUSTC_WRAPPER: sccache
   CARGO_TERM_COLOR: always
+  CARGO_NET_RETRY: 10
+  CARGO_NET_GIT_FETCH_WITH_CLI: true
   AWS_LC_SYS_PREBUILT_NASM: 1
 
 concurrency:
@@ -43,7 +45,7 @@ jobs:
     if: github.event_name == 'push' || inputs.Docker
     steps:
       - name: Install Cosign
-        uses: sigstore/cosign-installer@v4.1.1
+        uses: sigstore/cosign-installer@v4.1.2
       - name: Log In to GitHub Container Registry
         uses: docker/login-action@v4
         with:
@@ -113,50 +115,80 @@ jobs:
       matrix:
         include:
           - target: x86_64-unknown-linux-gnu
+            runner: ubuntu-latest
             platform: linux/amd64
             suffix: ""
           - target: x86_64-unknown-linux-musl
+            runner: ubuntu-latest
             platform: linux/amd64
             suffix: "-alpine"
           - target: aarch64-unknown-linux-gnu
+            runner: ubuntu-24.04-arm
             platform: linux/arm64
             suffix: ""
           - target: aarch64-unknown-linux-musl
+            runner: ubuntu-24.04-arm
             platform: linux/arm64
             suffix: "-alpine"
           - target: armv7-unknown-linux-gnueabihf
+            runner: ubuntu-latest
             platform: linux/arm/v7
             suffix: ""
           - target: armv7-unknown-linux-musleabihf
+            runner: ubuntu-latest
             platform: linux/arm/v7
             suffix: "-alpine"
           - target: arm-unknown-linux-gnueabihf
+            runner: ubuntu-latest
             platform: linux/arm/v6
             suffix: ""
           - target: arm-unknown-linux-musleabihf
+            runner: ubuntu-latest
             platform: linux/arm/v6
             suffix: "-alpine"
     name: Build / ${{matrix.target}}
-    runs-on: ubuntu-latest
+    runs-on: ${{matrix.runner}}
+    timeout-minutes: 180
     steps:
       - name: Checkout
-        uses: actions/checkout@v6.0.2
+        uses: actions/checkout@v7
+
+      - name: Free disk space (heavy ARM targets)
+        if: contains(matrix.target, 'arm') || contains(matrix.target, 'aarch64')
+        run: |
+          df -h /mnt /
+          sudo rm -rf /usr/share/dotnet /opt/ghc /usr/local/lib/android /usr/local/.ghcup /usr/local/share/powershell /usr/share/swift /opt/hostedtoolcache/CodeQL
+          sudo docker image prune --all --force || true
+          df -h /mnt /
 
       - name: Add swap (heavy ARM targets)
-        if: contains(matrix.target, 'arm')
+        if: contains(matrix.target, 'arm') || contains(matrix.target, 'aarch64')
         run: |
-          sudo fallocate -l 16G /mnt/swapfile
+          swap_dir=""
-          sudo chmod 600 /mnt/swapfile
+          for dir in /mnt /; do
-          sudo mkswap /mnt/swapfile
+            if [ -d "$dir" ] && [ "$(df --output=avail -k "$dir" | tail -1)" -ge 18874368 ]; then
-          sudo swapon /mnt/swapfile
+              swap_dir="$dir"
+              break
+            fi
+          done
+          if [ -z "$swap_dir" ]; then
+            echo "Insufficient space for swap on /mnt or /, aborting swap setup"
+            df -h
+            exit 1
+          fi
+          sudo fallocate -l 16G "${swap_dir%/}/swapfile"
+          sudo chmod 600 "${swap_dir%/}/swapfile"
+          sudo mkswap "${swap_dir%/}/swapfile"
+          sudo swapon "${swap_dir%/}/swapfile"
           sudo sysctl vm.swappiness=80
           free -h
           swapon --show
 
       - name: Set up QEMU
+        if: startsWith(matrix.platform, 'linux/arm/')
         uses: docker/setup-qemu-action@v4
         with:
-          platforms: "arm64,arm"
+          platforms: "arm"
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
@@ -175,6 +207,7 @@ jobs:
           password: ${{github.token}}
 
       - name: Log In to DockerHub
+        if: github.event_name == 'push' || inputs.Docker
         uses: docker/login-action@v4
         with:
           username: ${{secrets.DOCKERHUB_USERNAME}}
@@ -186,16 +219,16 @@ jobs:
           echo "checksum=$(yq -p toml -oy '.package[] | select((.source | contains("")) or (.checksum | contains("")))' Cargo.lock | sha256sum | awk '{print $1}')" >> "$GITHUB_OUTPUT"
 
       - name: Cache apt
-        uses: actions/cache@v5.0.5
+        uses: actions/cache@v6.1.0
         id: apt-cache
         with:
           path: |
             var-cache-apt
             var-lib-apt
-          key: apt-cache-${{ hashFiles('Dockerfile.build') }}
+          key: apt-cache-${{ runner.arch }}-${{ hashFiles('Dockerfile.build') }}
 
       - name: Cache Cargo
-        uses: actions/cache@v5.0.5
+        uses: actions/cache@v6.1.0
         id: cargo-cache
         with:
           path: |
@@ -204,7 +237,7 @@ jobs:
           key: cargo-cache-${{ steps.cal-dep-shasum.outputs.checksum }}
 
       - name: Inject cache into docker
-        uses: reproducible-containers/buildkit-cache-dance@v3.3.2
+        uses: reproducible-containers/buildkit-cache-dance@v3.4.0
         with:
           cache-map: |
             {
@@ -229,6 +262,7 @@ jobs:
             type=ref,event=branch,prefix=branch-
             type=edge,branch=main
             type=semver,pattern=v{{major}}.{{minor}}
+            type=semver,pattern=v{{major}}
 
       - name: Build Artifact
         id: bake
@@ -251,7 +285,7 @@ jobs:
           targets: ${{(github.event_name == 'push' || inputs.Docker) && 'build,image' || 'build'}}
 
       - name: Upload Artifacts
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         with:
           name: artifact-${{matrix.target}}
           path: |
@@ -268,7 +302,7 @@ jobs:
 
       - name: Upload digest
         if: github.event_name == 'push' || inputs.Docker
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         with:
           name: digests-${{matrix.suffix == '' && 'gnu' || 'musl'}}-${{ matrix.target }}
           path: ${{ runner.temp }}/digests/*
@@ -276,7 +310,7 @@ jobs:
           retention-days: 1
 
       - name: Upload GNU meta bake definition
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         if: (github.event_name == 'push' || inputs.Docker) && endsWith(matrix.target,'gnu') && startsWith(matrix.target,'x86')
         with:
           name: bake-meta-gnu
@@ -285,7 +319,7 @@ jobs:
           retention-days: 1
 
       - name: Upload musl meta bake definition
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         if: (github.event_name == 'push' || inputs.Docker) && endsWith(matrix.target,'musl') && startsWith(matrix.target,'x86')
         with:
           name: bake-meta-musl
@@ -303,10 +337,10 @@ jobs:
           - target: x86_64-pc-windows-msvc
     steps:
       - name: Checkout
-        uses: actions/checkout@v6.0.2
+        uses: actions/checkout@v7
 
       - name: Run sccache-cache
-        uses: mozilla-actions/sccache-action@v0.0.9
+        uses: mozilla-actions/sccache-action@v0.0.11
         with:
           disable_annotations: true
 
@@ -318,7 +352,7 @@ jobs:
           mv ./target/${{matrix.target}}/release/proxy.exe ./artifacts/proxy.exe
 
       - name: Upload Artifacts
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         with:
           name: artifact-${{matrix.target}}
           path: artifacts
@@ -334,10 +368,10 @@ jobs:
           - target: x86_64-apple-darwin
     steps:
       - name: Checkout
-        uses: actions/checkout@v6.0.2
+        uses: actions/checkout@v7
 
       - name: Run sccache-cache
-        uses: mozilla-actions/sccache-action@v0.0.9
+        uses: mozilla-actions/sccache-action@v0.0.11
         with:
           disable_annotations: true
 
@@ -349,7 +383,7 @@ jobs:
           mv ./target/${{matrix.target}}/release/proxy ./artifacts/proxy
 
       - name: Upload Artifacts
-        uses: actions/upload-artifact@v7
+        uses: actions/upload-artifact@v7.0.1
         with:
           name: artifact-${{matrix.target}}
           path: artifacts
@@ -367,7 +401,7 @@ jobs:
       # Must run before artifacts are downloaded: checkout cleans the workspace.
       - name: Checkout (for CHANGELOG)
         if: startsWith(github.ref, 'refs/tags/')
-        uses: actions/checkout@v6.0.2
+        uses: actions/checkout@v7
 
       - name: Download Artifacts
         uses: actions/download-artifact@v8
@@ -410,7 +444,7 @@ jobs:
             archive/**/*.zip
 
       - name: Use cosign to sign existing artifacts
-        uses: sigstore/gh-action-sigstore-python@v3.3.0
+        uses: sigstore/gh-action-sigstore-python@v3.5.0
         with:
           inputs: |
             archive/**/*.tar.gz
@@ -461,7 +495,7 @@ jobs:
   cleanup:
     name: Cleanup failed release
     needs: [linux, windows, macos, multiarch, release]
-    if: failure() && startsWith(github.ref, 'refs/tags/')
+    if: failure() && startsWith(github.ref, 'refs/tags/') && github.run_attempt >= 3
     runs-on: ubuntu-latest
     permissions:
       contents: write

.gitignore

@@ -3,3 +3,4 @@
 *.md
 !CHANGELOG.md
 !README.md
+__pycache__/

CHANGELOG.md

@@ -2,6 +2,40 @@
 
 All notable changes to this project will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [1.0.5] - 2026-10-25
+
+### Added
+
+### Changed
+- Replaced `base64` with `encodify`.
+- An HTTP route's `fallback` is now honoured: unmatched or unmapped requests on that route go to the fallback destination instead of `routing.default_destination`. A `fallback` naming an undeclared destination, or one that does not declare the `http` protocol, is rejected at startup.
+- A login held by `POST /connections/delay` now resolves its destination when the hold ends instead of before it.
+- `PUT /mappings`, `DELETE /mappings` and `POST /cache/invalidate?identifier=` end the login delay of that identifier; `POST /mappings/reload` and `POST /cache/invalidate` without an identifier end every login delay. Held logins proceed at once to the newly mapped destination.
+- Calling `POST /connections/delay` again for an identifier also moves the hold deadline of logins already waiting (still capped at 120 seconds per login).
+
+### Fixed
+- The sample configuration written by `install.sh` and `resources/config.sample.toml` named an undeclared HTTP route fallback (`default`) and failed startup validation.
+- `resources/config.stalwart-upgrade.toml` now documents the WebUI OAuth client identifiers (`https://<host>/admin/oauth-client.json`, `https://<host>/account/oauth-client.json`) and pins `/admin`, `/account`, `/api/auth/**` to the new deployment.
+- The `POST /config/reload` response no longer claims that cache capacity and TTLs require a restart; a reload rebuilds the router and its cache.
+- `POST /connections/delay` with a `seconds` value too large to represent now returns `400` instead of panicking.
+
+## [1.0.4] - 2026-09-10
+
+### Added
+
+### Changed
+- HTTP and JMAP connections are pinned to the account that authenticated them.
+- HTTP and JMAP routing identifiers are split on `routing.master_user_separators`.
+- A backend authentication failure now counts towards `listener.max_auth_attempts`.
+
+### Fixed
+- A backend authentication failure no longer leaves the client bridged to the backend unparsed.
+- `POST /connections/kick` now covers HTTP and JMAP sessions, including upgraded WebSocket bridges.
+- `POST /connections/delay` now covers HTTP and JMAP logins.
+- A rejected SASL response is no longer re-parsed as a command, which charged two authentication failures for one client mistake and could drop a command pipelined behind it.
+- An empty routing identifier is no longer treated as an account, so it is neither registered nor used to pin an HTTP connection.
+- A backend leg rejected at authentication is now closed with the protocol's logout command instead of having its socket dropped.
+
 ## [1.0.3] - 2026-08-30
 
 ### Added
@@ -24,22 +58,18 @@ All notable changes to this project will be documented in this file. This projec
 ## [1.0.1] - 2026-07-30
 
 ### Added
-- `server.host_down_min_clients`: number of distinct client addresses a
+- `server.host_down_min_clients`: number of distinct client addresses a failure streak must span before client-attributable failures can mark a destination down.
-  failure streak must span before client-attributable failures can mark a destination
-  down.
 - `GET /destinations` now also reports `failure_sources` and `host_level_failure`.
 
 ### Changed
 
 ### Fixed
-- The circuit breaker no longer marks a destination down because a backend rejects
+- The circuit breaker no longer marks a destination down because a backend rejects the connections of a single banned client (#2).
-  the connections of a single banned client (#2).
 
 ## [1.0.0] - 2026-06-08
 
 ### Added
-- Initial release of the migration proxy: pre-auth routing and socket bridging
+- Initial release of the migration proxy: pre-auth routing and socket bridging for SMTP, submission, LMTP, IMAP, POP3, ManageSieve and HTTP/HTTPS.
-  for SMTP, submission, LMTP, IMAP, POP3, ManageSieve and HTTP/HTTPS.
 
 ### Changed
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "proxy"
-version = "1.0.3"
+version = "1.0.5"
 edition = "2024"
 license = "AGPL-3.0-only OR LicenseRef-SEL"
 description = "Multi-protocol e-mail proxy"
@@ -22,10 +22,9 @@ tokio-rustls = { version = "0.26", default-features = false, features = ["aws_lc
 rustls-pemfile = "2.2"
 rustls-pki-types = "1.15"
 aws-lc-rs = "1.17"
-proxy-header = { version = "0.1.2", features = ["tokio"] }
+proxy-header = { version = "0.1", features = ["tokio"] }
 smtp-proto = "0.2.2"
-mail-parser = "0.11"
+encodify = "1.0"
-base64 = "0.23"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 toml = "1"

Dockerfile.build

@@ -9,6 +9,8 @@ FROM --platform=$BUILDPLATFORM rust:slim-trixie AS base
 ENV DEBIAN_FRONTEND="noninteractive" \
     BINSTALL_DISABLE_TELEMETRY=true \
     CARGO_TERM_COLOR=always \
+    CARGO_NET_RETRY=10 \
+    CARGO_NET_GIT_FETCH_WITH_CLI=true \
     LANG=C.UTF-8 \
     TZ=UTC \
     TERM=xterm-256color \
@@ -21,21 +23,36 @@ RUN \
     rm -f /etc/apt/apt.conf.d/docker-clean && \
     echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' >/etc/apt/apt.conf.d/keep-cache && \
     apt-get update && \
-    apt-get install -yq --no-install-recommends ca-certificates curl jq xz-utils make libclang-19-dev
+    apt-get install -yq --no-install-recommends ca-certificates curl git jq xz-utils make libclang-19-dev
-# Zig is pinned to 0.13.0. Zig 0.14+ changed how its default target ABI is
-# resolved for `x86_64-linux-gnu`-style triples, and on this dependency tree
-# (aws-lc-sys, libsqlite3-sys, rust-std 1.87+) that surfaces as ld.lld
-# undefined references to glibc 2.33+ symbols. Zig 0.13 produces binaries with
-# a max glibc ref of ~2.28 which stays compatible with Debian 11 / RHEL 8.
 RUN \
-    ZIG_VERSION=0.13.0 && \
+    ZIG_VERSION=0.17.0 && \
-    curl --retry 5 -fsSL "https://ziglang.org/download/${ZIG_VERSION}/zig-linux-$(uname -m)-${ZIG_VERSION}.tar.xz" | tar -J -x -C /usr/local && \
+    case "$(uname -m)" in \
-    ln -s "/usr/local/zig-linux-$(uname -m)-${ZIG_VERSION}/zig" /usr/local/bin/zig && \
+        x86_64) ZIG_SHA256=1cbe9df9f27e6b78d14ccbca43b6703a404ef79ef1c463de901d7f088d4e2026 ;; \
+        aarch64) ZIG_SHA256=9e8d11661d4ae3bd57702a3832781e23ad151dde5798e16a5ccd503f65234ff8 ;; \
+        *) exit 1 ;; \
+    esac && \
+    curl --retry 5 -fsSLo /tmp/zig.tar.xz "https://ziglang.org/download/${ZIG_VERSION}/zig-$(uname -m)-linux-${ZIG_VERSION}.tar.xz" && \
+    echo "${ZIG_SHA256}  /tmp/zig.tar.xz" | sha256sum -c - && \
+    tar -J -x -C /usr/local -f /tmp/zig.tar.xz && \
+    rm /tmp/zig.tar.xz && \
+    ln -s "/usr/local/zig-$(uname -m)-linux-${ZIG_VERSION}/zig" /usr/local/bin/zig && \
     zig version
 # Install cargo-binstall
 RUN curl --retry 5 -fL --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/cargo-bins/cargo-binstall/main/install-from-binstall-release.sh | bash
-# Install cargo-chef & sccache & cargo-zigbuild
+# Install cargo-chef & sccache. Versions are pinned so that an
-RUN cargo binstall --no-confirm cargo-chef sccache cargo-zigbuild
+# upstream release without prebuilt binaries for this platform cannot silently
+# turn this into a from-source build, and the `compile` strategy is disabled
+# because that fallback needs an OpenSSL toolchain this image does not carry:
+# it burns minutes and then fails. A transient GitHub fetch failure is retried.
+RUN \
+    for attempt in 1 2 3; do \
+        cargo binstall --no-confirm --disable-strategies compile \
+            cargo-chef@0.1.78 sccache@0.17.0 && break; \
+        echo "cargo binstall attempt ${attempt} failed, retrying"; \
+        sleep $((attempt * 15)); \
+    done && \
+    command -v cargo-chef && command -v sccache
+RUN cargo install --locked --git https://github.com/rust-cross/cargo-zigbuild --rev d9f7fd32fbac13cc26d23847835f7f23a5ed3a25 cargo-zigbuild
 
 # *****************
 # Planner
@@ -54,6 +71,7 @@ WORKDIR /app
 COPY --from=planner /app/recipe.json recipe.json
 ARG TARGET
 ARG BUILD_ENV
+ARG GLIBC_VERSION=2.28
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 # Install toolchain and specify some env variables
 RUN \
@@ -61,6 +79,13 @@ RUN \
     rustup target add ${TARGET} && \
     mkdir -p artifact && \
     touch /env-cargo && \
+    if [[ "${TARGET}" == *-gnu* ]]; then \
+        echo "export BUILD_TARGET=${TARGET}.${GLIBC_VERSION}" >> /env-cargo; \
+        mkdir -p target && \
+        ln -s "${TARGET}" "target/${TARGET}.${GLIBC_VERSION}"; \
+    else \
+        echo "export BUILD_TARGET=${TARGET}" >> /env-cargo; \
+    fi && \
     if [ ! -z "${BUILD_ENV}" ]; then \
         echo "export ${BUILD_ENV}" >> /env-cargo; \
         echo "Setting up ${BUILD_ENV}"; \
@@ -72,7 +97,7 @@ RUN \
     --mount=type=cache,target=/usr/local/cargo/registry \
     --mount=type=cache,target=/usr/local/cargo/git \
     source /env-cargo && \
-    cargo chef cook --recipe-path recipe.json --zigbuild --release --target ${TARGET} -p proxy
+    cargo chef cook --recipe-path recipe.json --zigbuild --release --target ${BUILD_TARGET} -p proxy
 # Copy the source code
 COPY . .
 ENV RUSTC_WRAPPER="sccache" \
@@ -84,7 +109,7 @@ RUN \
     --mount=type=cache,target=/usr/local/cargo/registry \
     --mount=type=cache,target=/usr/local/cargo/git \
     source /env-cargo && \
-    cargo zigbuild --release --target ${TARGET} -p proxy && \
+    cargo zigbuild --release --target ${BUILD_TARGET} -p proxy && \
     mv /app/target/${TARGET}/release/proxy /app/artifact/proxy
 
 # *****************

install.sh

@@ -266,8 +266,8 @@ tls = "implicit"
 port = 995
 tls = "implicit"
 [destination.stalwart.protocol.submission]
-port = 587
+port = 465
-tls = "starttls"
+tls = "implicit"
 [destination.stalwart.protocol.managesieve]
 port = 4190
 tls = "starttls"
@@ -277,37 +277,37 @@ tls = "implicit"
 
 [listener.imap]
 protocol = "imap"
-bind = ["0.0.0.0:993", "[::]:993"]
+bind = ["[::]:993"]
 tls = "implicit"
 
 [listener.imap-starttls]
 protocol = "imap"
-bind = ["0.0.0.0:143", "[::]:143"]
+bind = ["[::]:143"]
 tls = "starttls"
 
 [listener.pop3]
 protocol = "pop3"
-bind = ["0.0.0.0:995", "[::]:995"]
+bind = ["[::]:995"]
 tls = "implicit"
 
 [listener.submission]
 protocol = "submission"
-bind = ["0.0.0.0:587", "[::]:587"]
+bind = ["[::]:587"]
 tls = "starttls"
 
 [listener.submissions]
 protocol = "submission"
-bind = ["0.0.0.0:465", "[::]:465"]
+bind = ["[::]:465"]
 tls = "implicit"
 
 [listener.managesieve]
 protocol = "managesieve"
-bind = ["0.0.0.0:4190", "[::]:4190"]
+bind = ["[::]:4190"]
 tls = "starttls"
 
 [listener.https]
 protocol = "http"
-bind = ["0.0.0.0:443", "[::]:443"]
+bind = ["[::]:443"]
 tls = "implicit"
 forwarded = "off"
 
@@ -318,7 +318,7 @@ destination = "legacy"
 [[http.route]]
 match = "/**"
 extract = { from = "authorization" }
-fallback = "default"
+fallback = "legacy"
 
 [admin]
 bind = "127.0.0.1:9443"

resources/config.dovecot-postfix.toml

@@ -112,8 +112,8 @@ tls = "implicit"
 port = 995
 tls = "implicit"
 [destination.stalwart.protocol.submission]
-port = 587
+port = 465
-tls = "starttls"
+tls = "implicit"
 [destination.stalwart.protocol.managesieve]
 port = 4190
 tls = "starttls"
@@ -129,38 +129,45 @@ tls = "plain"
 # here. Once accounts are on Stalwart, JMAP and the web interface are served by
 # the new server; an HTTP listener routing to "stalwart" can be added at that
 # point if a single hostname for web access is wanted.
+#
+# Each listener binds [::] only: on Linux and macOS that socket also accepts
+# IPv4 clients, and on Linux a second 0.0.0.0 entry for the same port fails
+# with "Address already in use". Where IPv6 sockets are IPv6-only (FreeBSD by
+# default, or net.ipv6.bindv6only = 1 on Linux), add "0.0.0.0:<port>" to each
+# bind list. On a host whose kernel has IPv6 disabled, [::] cannot be bound:
+# use "0.0.0.0:<port>" instead.
 # ---------------------------------------------------------------------------
 [listener.imaps]
 protocol = "imap"
-bind = ["0.0.0.0:993", "[::]:993"]
+bind = ["[::]:993"]
 tls = "implicit"
 [listener.imap]
 protocol = "imap"
-bind = ["0.0.0.0:143", "[::]:143"]
+bind = ["[::]:143"]
 tls = "starttls"
 [listener.pop3s]
 protocol = "pop3"
-bind = ["0.0.0.0:995", "[::]:995"]
+bind = ["[::]:995"]
 tls = "implicit"
 [listener.pop3]
 protocol = "pop3"
-bind = ["0.0.0.0:110", "[::]:110"]
+bind = ["[::]:110"]
 tls = "starttls"
 [listener.submission]
 protocol = "submission"
-bind = ["0.0.0.0:587", "[::]:587"]
+bind = ["[::]:587"]
 tls = "starttls"
 [listener.submissions]
 protocol = "submission"
-bind = ["0.0.0.0:465", "[::]:465"]
+bind = ["[::]:465"]
 tls = "implicit"
 [listener.managesieve]
 protocol = "managesieve"
-bind = ["0.0.0.0:4190", "[::]:4190"]
+bind = ["[::]:4190"]
 tls = "starttls"
 [listener.smtp]
 protocol = "smtp"
-bind = ["0.0.0.0:25", "[::]:25"]
+bind = ["[::]:25"]
 tls = "plain"
 
 # ---------------------------------------------------------------------------

resources/config.sample.toml

@@ -92,8 +92,8 @@ tls = "implicit"
 port = 995
 tls = "implicit"
 [destination.stalwart.protocol.submission]
-port = 587
+port = 465
-tls = "starttls"
+tls = "implicit"
 [destination.stalwart.protocol.managesieve]
 port = 4190
 tls = "starttls"
@@ -104,40 +104,47 @@ tls = "implicit"
 # ---------------------------------------------------------------------------
 # Listeners: one entry per protocol + TLS mode + bind set.
 # tls = "implicit" | "starttls" | "plain".
+#
+# Each listener binds [::] only: on Linux and macOS that socket also accepts
+# IPv4 clients, and on Linux a second 0.0.0.0 entry for the same port fails
+# with "Address already in use". Where IPv6 sockets are IPv6-only (FreeBSD by
+# default, or net.ipv6.bindv6only = 1 on Linux), add "0.0.0.0:<port>" to each
+# bind list. On a host whose kernel has IPv6 disabled, [::] cannot be bound:
+# use "0.0.0.0:<port>" instead.
 # ---------------------------------------------------------------------------
 [listener.imap]
 protocol = "imap"
-bind = ["0.0.0.0:993", "[::]:993"]
+bind = ["[::]:993"]
 tls = "implicit"
 
 [listener.imap-starttls]
 protocol = "imap"
-bind = ["0.0.0.0:143", "[::]:143"]
+bind = ["[::]:143"]
 tls = "starttls"
 
 [listener.pop3]
 protocol = "pop3"
-bind = ["0.0.0.0:995", "[::]:995"]
+bind = ["[::]:995"]
 tls = "implicit"
 
 [listener.submission]
 protocol = "submission"
-bind = ["0.0.0.0:587", "[::]:587"]
+bind = ["[::]:587"]
 tls = "starttls"
 
 [listener.submissions]
 protocol = "submission"
-bind = ["0.0.0.0:465", "[::]:465"]
+bind = ["[::]:465"]
 tls = "implicit"
 
 [listener.managesieve]
 protocol = "managesieve"
-bind = ["0.0.0.0:4190", "[::]:4190"]
+bind = ["[::]:4190"]
 tls = "starttls"
 
 [listener.https]
 protocol = "http"
-bind = ["0.0.0.0:443", "[::]:443"]
+bind = ["[::]:443"]
 tls = "implicit"
 forwarded = "off"
 
@@ -152,7 +159,7 @@ destination = "legacy"
 [[http.route]]
 match = "/**"
 extract = { from = "authorization" }
-fallback = "default"
+fallback = "legacy"
 
 # ---------------------------------------------------------------------------
 # Admin listener: the cache-integrity boundary. Bind to loopback or a dedicated

resources/config.stalwart-upgrade.toml

@@ -100,8 +100,8 @@ tls = "implicit"
 port = 995
 tls = "implicit"
 [destination.old.protocol.submission]
-port = 587
+port = 465
-tls = "starttls"
+tls = "implicit"
 [destination.old.protocol.managesieve]
 port = 4190
 tls = "starttls"
@@ -124,8 +124,8 @@ tls = "implicit"
 port = 995
 tls = "implicit"
 [destination.new.protocol.submission]
-port = 587
+port = 465
-tls = "starttls"
+tls = "implicit"
 [destination.new.protocol.managesieve]
 port = 4190
 tls = "starttls"
@@ -165,12 +165,21 @@ destination = "old"
 match = "/api/auth"
 destination = "new"
 [[http.route]]
+match = "/api/auth/**"
+destination = "new"
+[[http.route]]
 match = "/api/discover/**"
 destination = "new"
 [[http.route]]
+match = "/admin"
+destination = "new"
+[[http.route]]
 match = "/admin/**"
 destination = "new"
 [[http.route]]
+match = "/account"
+destination = "new"
+[[http.route]]
 match = "/account/**"
 destination = "new"
 [[http.route]]
@@ -181,53 +190,63 @@ match = "/device"
 destination = "new"
 
 # OAuth token exchange is shared; route it by the web client that requested it.
-# Add matching mapping entries:  webadmin  old   and   stalwart-webui  new
+# Add matching mapping entries (replace the hostname with the public one):
+#   webadmin                                             old
+#   https://mail.example.org/admin/oauth-client.json     new
+#   https://mail.example.org/account/oauth-client.json   new
 [[http.route]]
 match = "/auth/token"
 extract = { from = "body", regex = "client_id=([^&]+)" }
 fallback = "old"
 
-# Everything else: route by the authenticated account, fall back to default.
+# Everything else: route by the authenticated account, fall back to the old deployment.
 [[http.route]]
 match = "/**"
 extract = { from = "authorization" }
-fallback = "default"
+fallback = "old"
 
 # ---------------------------------------------------------------------------
 # Listeners: the public ports clients connect to. These take over the ports the
 # old server used to answer on directly.
+#
+# Each listener binds [::] only: on Linux and macOS that socket also accepts
+# IPv4 clients, and on Linux a second 0.0.0.0 entry for the same port fails
+# with "Address already in use". Where IPv6 sockets are IPv6-only (FreeBSD by
+# default, or net.ipv6.bindv6only = 1 on Linux), add "0.0.0.0:<port>" to each
+# bind list. On a host whose kernel has IPv6 disabled, [::] cannot be bound:
+# use "0.0.0.0:<port>" instead.
 # ---------------------------------------------------------------------------
 [listener.imaps]
 protocol = "imap"
-bind = ["0.0.0.0:993", "[::]:993"]
+bind = ["[::]:993"]
 tls = "implicit"
 [listener.imap]
 protocol = "imap"
-bind = ["0.0.0.0:143", "[::]:143"]
+bind = ["[::]:143"]
 tls = "starttls"
 [listener.pop3s]
 protocol = "pop3"
-bind = ["0.0.0.0:995", "[::]:995"]
+bind = ["[::]:995"]
 tls = "implicit"
 [listener.pop3]
 protocol = "pop3"
-bind = ["0.0.0.0:110", "[::]:110"]
+bind = ["[::]:110"]
 tls = "starttls"
 [listener.submission]
 protocol = "submission"
-bind = ["0.0.0.0:587", "[::]:587"]
+bind = ["[::]:587"]
 tls = "starttls"
 [listener.submissions]
 protocol = "submission"
-bind = ["0.0.0.0:465", "[::]:465"]
+bind = ["[::]:465"]
 tls = "implicit"
 [listener.managesieve]
 protocol = "managesieve"
-bind = ["0.0.0.0:4190", "[::]:4190"]
+bind = ["[::]:4190"]
 tls = "starttls"
 [listener.https]
 protocol = "http"
-bind = ["0.0.0.0:443", "[::]:443"]
+bind = ["[::]:443"]
 tls = "implicit"
 # Strip any Forwarded / X-Forwarded-For headers arriving from clients rather
 # than trusting them; the proxy sets its own based on the real peer.
@@ -236,7 +255,7 @@ forwarded = "off"
 # a pass-through listener cannot offer STARTTLS.
 [listener.smtp]
 protocol = "smtp"
-bind = ["0.0.0.0:25", "[::]:25"]
+bind = ["[::]:25"]
 tls = "plain"
 
 # ---------------------------------------------------------------------------

resources/migrate_v016_to_plan.py

@@ -0,0 +1,331 @@
+#!/usr/bin/env python3
+
+import argparse
+import base64
+import json
+import os
+import ssl
+import sys
+import urllib.error
+import urllib.parse
+import urllib.request
+
+REQUEST_TIMEOUT = 60
+DEFAULT_PAGE_SIZE = 500
+MASKED = "****"
+USING = ["urn:ietf:params:jmap:core", "urn:stalwart:jmap"]
+COPIED_FIELDS = ("description", "quotas", "locale", "timeZone")
+
+
+class ApiError(RuntimeError):
+    pass
+
+
+class StalwartV016Client:
+    def __init__(self, url, token=None, username=None, password=None, insecure=False):
+        self.base = url.rstrip("/")
+        if token:
+            self.auth = "Bearer " + token
+        elif username is not None:
+            raw = f"{username}:{password or ''}".encode()
+            self.auth = "Basic " + base64.b64encode(raw).decode()
+        else:
+            raise ValueError("either a token or a username must be provided")
+        self.ctx = None
+        if insecure:
+            self.ctx = ssl.create_default_context()
+            self.ctx.check_hostname = False
+            self.ctx.verify_mode = ssl.CERT_NONE
+        self.api_url = None
+        self.page_size = DEFAULT_PAGE_SIZE
+
+    def request(self, url, body=None):
+        data = json.dumps(body).encode() if body is not None else None
+        req = urllib.request.Request(url, data=data, method="POST" if data else "GET")
+        req.add_header("Authorization", self.auth)
+        req.add_header("Accept", "application/json")
+        if data:
+            req.add_header("Content-Type", "application/json")
+        try:
+            with urllib.request.urlopen(req, timeout=REQUEST_TIMEOUT, context=self.ctx) as resp:
+                return json.loads(resp.read().decode())
+        except urllib.error.HTTPError as exc:
+            detail = exc.read().decode(errors="replace")
+            raise ApiError(f"{exc.code} {exc.reason} for {url}: {detail}") from exc
+        except urllib.error.URLError as exc:
+            raise ApiError(f"cannot reach {url}: {exc.reason}") from exc
+
+    def connect(self):
+        session = self.request(self.base + "/.well-known/jmap")
+        api_url = session.get("apiUrl")
+        if not api_url:
+            raise ApiError("the JMAP session does not advertise an apiUrl")
+        self.api_url = self.base + (urllib.parse.urlsplit(api_url).path or "/jmap")
+        core = (session.get("capabilities") or {}).get("urn:ietf:params:jmap:core") or {}
+        max_get = core.get("maxObjectsInGet")
+        if isinstance(max_get, int) and max_get > 0:
+            self.page_size = min(DEFAULT_PAGE_SIZE, max_get)
+
+    def call(self, method, args):
+        resp = self.request(self.api_url, {"using": USING, "methodCalls": [[method, args, "c0"]]})
+        responses = resp.get("methodResponses") or []
+        if len(responses) != 1:
+            raise ApiError(f"{method}: unexpected response {resp}")
+        name, result, _ = responses[0]
+        if name == "error":
+            raise ApiError(f"{method}: {result.get('type')}: {result.get('description', '')}")
+        return result
+
+    def query_ids(self, obj):
+        ids = []
+        args = {"limit": self.page_size}
+        while True:
+            batch = self.call(f"x:{obj}/query", args).get("ids") or []
+            ids.extend(batch)
+            if len(batch) < self.page_size:
+                return ids
+            args = {"limit": self.page_size, "anchor": batch[-1], "anchorOffset": 1}
+
+    def get_all(self, obj):
+        objects = []
+        ids = self.query_ids(obj)
+        for start in range(0, len(ids), self.page_size):
+            result = self.call(f"x:{obj}/get", {"ids": ids[start : start + self.page_size]})
+            objects.extend(result.get("list") or [])
+        return objects
+
+
+def entries(value):
+    if isinstance(value, list):
+        return value
+    if isinstance(value, dict):
+        return [value[k] for k in sorted(value, key=lambda k: int(k) if k.isdigit() else k)]
+    return []
+
+
+def as_list_map(items):
+    return {str(i): item for i, item in enumerate(items)}
+
+
+def domain_ref(domain):
+    return "domain_" + "".join(c if c.isalnum() else "_" for c in domain)
+
+
+class PlanBuilder:
+    def __init__(self, domains, existing, warn):
+        self.domains = domains
+        self.existing = existing
+        self.warn = warn
+
+    def domain_target(self, domain_id, address, used):
+        name = self.domains.get(domain_id)
+        if name is None:
+            raise ApiError(f"{address}: references unknown domain id {domain_id}")
+        used.add(name)
+        return self.existing.get(name) or ("#" + domain_ref(name))
+
+    def credentials(self, account, address):
+        creds = []
+        skipped = 0
+        for cred in entries(account.get("credentials")):
+            if cred.get("@type") != "Password":
+                skipped += 1
+                continue
+            secret = cred.get("secret")
+            if not secret or secret == MASKED:
+                raise ApiError(
+                    f"{address}: the source returned a masked password; restart it with "
+                    "STALWART_INCLUDE_SECRETS=1 in its environment"
+                )
+            out = {"@type": "Password", "secret": secret}
+            otp = cred.get("otpAuth")
+            if otp and otp != MASKED:
+                out["otpUrl"] = otp
+            for key in ("expiresAt", "allowedIps"):
+                if cred.get(key):
+                    out[key] = cred[key]
+            creds.append(out)
+        if skipped:
+            self.warn(f"{address}: {skipped} app password(s) or API key(s) not migrated")
+        return creds
+
+    def account(self, account, address, used):
+        kind = account.get("@type")
+        out = {
+            "@type": kind,
+            "name": account["name"],
+            "domainId": self.domain_target(account["domainId"], address, used),
+        }
+        for key in COPIED_FIELDS:
+            if account.get(key) not in (None, {}, []):
+                out[key] = account[key]
+
+        if kind == "User":
+            creds = self.credentials(account, address)
+            if creds:
+                out["credentials"] = as_list_map(creds)
+            else:
+                self.warn(f"{address}: no password credential, the account is created without one")
+
+        roles = account.get("roles") or {}
+        if roles.get("@type") == "Custom":
+            fallback = "User" if kind == "User" else "Default"
+            self.warn(f"{address}: custom roles not migrated, assigned the {fallback} roles")
+            out["roles"] = {"@type": fallback}
+        elif roles:
+            out["roles"] = roles
+
+        permissions = account.get("permissions") or {}
+        if permissions.get("@type") in ("Merge", "Replace"):
+            self.warn(f"{address}: account-level permissions copied, check them on the target")
+            out["permissions"] = permissions
+
+        if kind == "User":
+            encryption = account.get("encryptionAtRest") or {}
+            if encryption.get("@type") not in (None, "Disabled"):
+                self.warn(f"{address}: encryption at rest not migrated, the public key must be added again")
+            out["encryptionAtRest"] = {"@type": "Disabled"}
+
+        if account.get("memberGroupIds"):
+            self.warn(f"{address}: group memberships not migrated")
+        if account.get("externalId"):
+            self.warn(f"{address}: external directory identifier not migrated")
+        if account.get("memberTenantId"):
+            self.warn(f"{address}: tenant membership not migrated")
+
+        aliases = []
+        for alias in entries(account.get("aliases")):
+            entry = {
+                "name": alias["name"],
+                "domainId": self.domain_target(alias["domainId"], address, used),
+                "enable": alias.get("enabled", True),
+            }
+            if alias.get("description"):
+                entry["description"] = alias["description"]
+            aliases.append(entry)
+        if aliases:
+            out["aliases"] = as_list_map(aliases)
+        return out
+
+
+def plan_lines(accounts, builder):
+    used = set()
+    value = {}
+    for address, account in accounts:
+        value["acct_" + str(account["id"])] = builder.account(account, address, used)
+    ops = []
+    missing = sorted(d for d in used if d not in builder.existing)
+    if missing:
+        ops.append(
+            {
+                "@type": "upsert",
+                "object": "Domain",
+                "matchOn": ["name"],
+                "value": {domain_ref(d): {"name": d} for d in missing},
+            }
+        )
+    ops.append({"@type": "create", "object": "Account", "value": value})
+    return [json.dumps(op) for op in ops]
+
+
+def write_lines(path, lines):
+    fd = os.open(path, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+    with os.fdopen(fd, "w") as out:
+        for line in lines:
+            out.write(line + "\n")
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Build Stalwart CLI plans that recreate the accounts of a Stalwart "
+        "v0.16.27 server, with their password hashes, on a Stalwart v1 server.",
+    )
+    parser.add_argument("addresses", nargs="*", help="export only these accounts (default: all)")
+    parser.add_argument("--url", required=True, help="base URL of the v0.16 server")
+    parser.add_argument("--token", help="admin bearer token")
+    parser.add_argument("--user", help="admin username (HTTP basic auth)")
+    parser.add_argument("--password", help="admin password (default: $SOURCE_ADMIN_PASSWORD)")
+    parser.add_argument("--insecure", action="store_true", help="skip TLS verification")
+    parser.add_argument("--include-groups", action="store_true", help="also export groups")
+    parser.add_argument(
+        "--existing-domain",
+        action="append",
+        default=[],
+        metavar="NAME=ID",
+        help="reference a target domain by id instead of matching it by name",
+    )
+    target = parser.add_mutually_exclusive_group()
+    target.add_argument("--output", help="write one plan to this file (default: stdout)")
+    target.add_argument("--output-dir", help="write one plan per account into this directory")
+    args = parser.parse_args()
+
+    if not args.token and args.user is None:
+        parser.error("provide --token or --user")
+    password = args.password if args.password is not None else os.environ.get("SOURCE_ADMIN_PASSWORD")
+
+    existing = {}
+    for entry in args.existing_domain:
+        name, sep, value = entry.partition("=")
+        if not sep:
+            parser.error(f"--existing-domain expects NAME=ID, got {entry!r}")
+        existing[name.strip().lower()] = value.strip()
+
+    client = StalwartV016Client(
+        args.url, token=args.token, username=args.user, password=password, insecure=args.insecure
+    )
+    client.connect()
+
+    domains = {d["id"]: d["name"].lower() for d in client.get_all("Domain")}
+    kinds = {"User", "Group"} if args.include_groups else {"User"}
+    accounts = {}
+    for account in client.get_all("Account"):
+        if account.get("@type") not in kinds:
+            continue
+        domain = domains.get(account.get("domainId"))
+        if domain:
+            accounts[f"{account['name']}@{domain}".lower()] = account
+
+    if args.addresses:
+        wanted = [a.lower() for a in args.addresses]
+        unknown = [a for a in wanted if a not in accounts]
+        if unknown:
+            sys.stderr.write("unknown account(s): " + ", ".join(unknown) + "\n")
+            return 1
+        selected = [(a, accounts[a]) for a in wanted]
+    else:
+        selected = sorted(accounts.items())
+
+    if not selected:
+        sys.stderr.write("no accounts to export\n")
+        return 1
+
+    warnings = []
+    builder = PlanBuilder(domains, existing, warnings.append)
+
+    if args.output_dir:
+        os.makedirs(args.output_dir, mode=0o700, exist_ok=True)
+        for address, account in selected:
+            write_lines(
+                os.path.join(args.output_dir, address + ".ndjson"),
+                plan_lines([(address, account)], builder),
+            )
+    else:
+        lines = plan_lines(selected, builder)
+        if args.output:
+            write_lines(args.output, lines)
+        else:
+            for line in lines:
+                sys.stdout.write(line + "\n")
+
+    for warning in warnings:
+        sys.stderr.write("warning: " + warning + "\n")
+    sys.stderr.write(f"exported {len(selected)} account(s)\n")
+    return 0
+
+
+if __name__ == "__main__":
+    try:
+        sys.exit(main())
+    except ApiError as exc:
+        sys.stderr.write(f"error: {exc}\n")
+        sys.exit(1)

src/admin.rs

@@ -303,6 +303,7 @@ async fn handle(
                     } else {
                         match ctx.router.upsert(&id, &dest).await {
                             Ok(()) => {
+                                ctx.conns.release_delay(&ctx.router.normalize(&id));
                                 tracing::info!(identifier = %crate::observe::redact(&id), %dest, "admin upserted mapping");
                                 write_response(&mut stream, 200, "OK", "ok\n").await?;
                             }
@@ -343,6 +344,7 @@ async fn handle(
                 } else {
                     match ctx.router.remove(&id).await {
                         Ok(existed) => {
+                            ctx.conns.release_delay(&ctx.router.normalize(&id));
                             tracing::info!(identifier = %crate::observe::redact(&id), existed, "admin removed mapping");
                             let body = if existed { "removed\n" } else { "absent\n" };
                             write_response(&mut stream, 200, "OK", body).await?;
@@ -379,7 +381,7 @@ async fn handle(
                     tracing::info!("admin reloaded configuration");
                     let body = serde_json::json!({
                         "reloaded": true,
-                        "note": "listener binds/protocols, admin bind/token, and cache capacity/TTLs require a restart to change",
+                        "note": "listener binds/protocols and admin bind/token require a restart to change",
                     })
                     .to_string();
                     write_json(&mut stream, 200, &body).await?;
@@ -400,10 +402,12 @@ async fn handle(
             match request.query_param("identifier") {
                 Some(id) => {
                     ctx.router.invalidate(&id).await;
+                    ctx.conns.release_delay(&ctx.router.normalize(&id));
                     tracing::info!(identifier = %crate::observe::redact(&id), "admin invalidated entry");
                 }
                 None => {
                     ctx.router.invalidate_all();
+                    ctx.conns.release_all_delays();
                     tracing::info!("admin invalidated entire cache");
                 }
             }
@@ -411,6 +415,7 @@ async fn handle(
         }
         ("POST", "/mappings/reload") => match ctx.router.reload().await {
             Ok(()) => {
+                ctx.conns.release_all_delays();
                 tracing::info!("admin reloaded mappings");
                 write_response(&mut stream, 200, "OK", "reloaded\n").await?;
             }
@@ -435,15 +440,17 @@ async fn handle(
                 request.query_param("identifier"),
                 request.query_param("seconds"),
             ) {
-                (Some(id), Some(secs)) => match secs.parse::<u64>() {
+                (Some(id), Some(secs)) => match secs.parse::<u64>().ok().and_then(|seconds| {
-                    Ok(seconds) => {
+                    std::time::Instant::now()
-                        let until =
+                        .checked_add(std::time::Duration::from_secs(seconds))
-                            std::time::Instant::now() + std::time::Duration::from_secs(seconds);
+                        .map(|until| (seconds, until))
+                }) {
+                    Some((seconds, until)) => {
                         ctx.conns.set_delay(&ctx.router.normalize(&id), until);
                         tracing::info!(identifier = %crate::observe::redact(&id), seconds, "admin set login delay");
                         write_response(&mut stream, 200, "OK", "ok\n").await?;
                     }
-                    Err(_) => {
+                    None => {
                         write_response(&mut stream, 400, "Bad Request", "invalid seconds\n")
                             .await?;
                     }

src/config/mod.rs

@@ -920,6 +920,14 @@ impl Config {
                     )));
                 }
             }
+            if let Some(fallback) = &route.fallback {
+                let dest = self.destination(fallback)?;
+                if !dest.protocol.contains_key(&Protocol::Http) {
+                    return Err(ProxyError::config(format!(
+                        "http route fallback {fallback:?} does not declare the http protocol"
+                    )));
+                }
+            }
             if let Some(extract) = &route.extract {
                 if extract.from == ExtractFrom::Body && extract.regex.is_none() {
                     return Err(ProxyError::config(

src/http/proxy.rs

@@ -5,6 +5,7 @@
  */
 
 use std::net::{IpAddr, SocketAddr};
+use std::sync::Arc;
 use std::time::Duration;
 
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
@@ -13,7 +14,7 @@ use tokio::time::timeout;
 use crate::config::{ForwardedMode, ListenerConfig, Protocol, TlsMode};
 use crate::error::{ProxyError, Result};
 use crate::net::BoxedStream;
-use crate::proto::common::Ctx;
+use crate::proto::common::{ConnGuard, Ctx};
 
 use super::head::{BodyFraming, Head, ParseError, ParseOutcome, error_response};
 use super::router::{HttpRouter, RouteOutcome};
@@ -379,12 +380,55 @@ fn response_no_body(req_method: &str, head: &Head) -> bool {
     matches!(head.framing, BodyFraming::None)
 }
 
+struct Account {
+    cancel: Option<tokio::sync::watch::Sender<bool>>,
+    guard: Option<ConnGuard>,
+    pinned: Option<String>,
+}
+
+impl Account {
+    fn new(cancel: tokio::sync::watch::Sender<bool>) -> Self {
+        Account {
+            cancel: Some(cancel),
+            guard: None,
+            pinned: None,
+        }
+    }
+
+    fn accepts(&self, ctx: &Ctx, identifier: Option<&str>) -> bool {
+        match (&self.pinned, identifier) {
+            (Some(pinned), Some(id)) => *pinned == ctx.router.normalize(id),
+            _ => true,
+        }
+    }
+
+    fn pin(&mut self, ctx: &Ctx, identifier: Option<&str>) -> bool {
+        if self.pinned.is_some() {
+            return false;
+        }
+        let Some(id) = identifier else {
+            return false;
+        };
+        let Some(cancel) = self.cancel.take() else {
+            return false;
+        };
+        self.pinned = Some(ctx.router.normalize(id));
+        self.guard = Some(ctx.register_conn_cancel(id, cancel));
+        true
+    }
+
+    fn into_guard(self) -> Option<ConnGuard> {
+        self.guard
+    }
+}
+
 enum Disposition {
     Close,
     Hijack {
         backend: BoxedStream,
         to_backend: Vec<u8>,
         to_client: Vec<u8>,
+        guard: Option<ConnGuard>,
     },
 }
 
@@ -400,7 +444,16 @@ pub async fn handle(
     local: SocketAddr,
 ) -> Result<()> {
     let bridge_idle = ctx.config.server.bridge_idle;
-    match serve(ctx, listener, &mut stream, peer, local).await {
+    let (cancel_tx, cancel_rx) = tokio::sync::watch::channel(false);
+
+    let served = tokio::select! {
+        result = serve(ctx, listener, &mut stream, peer, local, cancel_tx) => result,
+        _ = crate::outbound::wait_kick(Some(cancel_rx)) => {
+            return Err(ProxyError::backend("disconnected by admin"));
+        }
+    };
+
+    match served {
         Ok(Disposition::Close) => {
             shutdown_client(&mut stream).await;
             Ok(())
@@ -409,9 +462,18 @@ pub async fn handle(
             backend,
             to_backend,
             to_client,
+            guard,
         }) => {
-            crate::outbound::bridge(stream, backend, &to_backend, &to_client, bridge_idle, None)
+            let cancel = guard.as_ref().map(|g| g.cancel());
-                .await?;
+            crate::outbound::bridge(
+                stream,
+                backend,
+                &to_backend,
+                &to_client,
+                bridge_idle,
+                cancel,
+            )
+            .await?;
             Ok(())
         }
         Err(e) => Err(e),
@@ -424,6 +486,7 @@ async fn serve(
     stream: &mut BoxedStream,
     peer: SocketAddr,
     local: SocketAddr,
+    cancel: tokio::sync::watch::Sender<bool>,
 ) -> Result<Disposition> {
     let router = ctx.http_router.as_ref();
     let max_head = router.max_head_size;
@@ -459,7 +522,7 @@ async fn serve(
     let mut first_head = first_head;
     sanitize_inbound_forwarded(&mut first_head, listener);
 
-    let (buffered_body, dest_id) = match prepare(
+    let prepared = match prepare(
         ctx,
         router,
         stream,
@@ -477,6 +540,13 @@ async fn serve(
         }
     };
 
+    let mut account = Account::new(cancel);
+    if account.pin(ctx, prepared.identifier.as_deref()) {
+        crate::proto::common::hold_login(ctx, prepared.identifier.as_deref()).await;
+    }
+    let dest_id = prepared.destination(ctx).await;
+    let buffered_body = prepared.body;
+
     let (dest, ep, tls_cfg) = match ctx.endpoint(&dest_id, Protocol::Http) {
         Ok(t) => t,
         Err(_) => {
@@ -552,6 +622,7 @@ async fn serve(
                     backend,
                     to_backend,
                     to_client,
+                    guard: account.into_guard(),
                 });
             }
             Ok(ExchangeResult::Close) => return Ok(Disposition::Close),
@@ -576,7 +647,7 @@ async fn serve(
         let mut next = next;
         sanitize_inbound_forwarded(&mut next, listener);
 
-        let (next_body, next_dest) = match prepare(
+        let prepared = match prepare(
             ctx,
             router,
             stream,
@@ -594,7 +665,14 @@ async fn serve(
             }
         };
 
-        if next_dest != dest_id {
+        let misdirected = !account.accepts(ctx, prepared.identifier.as_deref()) || {
+            if account.pin(ctx, prepared.identifier.as_deref()) {
+                crate::proto::common::hold_login(ctx, prepared.identifier.as_deref()).await;
+            }
+            prepared.destination(ctx).await != dest_id
+        };
+        let next_body = prepared.body;
+        if misdirected {
             if let Some(body) = &next_body {
                 drain_buffered(stream, &mut reader, &next, body.len(), idle.body)
                     .await
@@ -891,6 +969,34 @@ async fn drain_buffered(
     Ok(())
 }
 
+enum Target {
+    Pinned(String),
+    Account { fallback: Option<Arc<str>> },
+}
+
+struct Prepared {
+    body: Option<Vec<u8>>,
+    target: Target,
+    identifier: Option<String>,
+}
+
+impl Prepared {
+    async fn destination(&self, ctx: &Ctx) -> String {
+        match &self.target {
+            Target::Pinned(dest_id) => dest_id.clone(),
+            Target::Account {
+                fallback: Some(fallback),
+            } => ctx
+                .resolve_or(self.identifier.as_deref(), fallback)
+                .await
+                .to_string(),
+            Target::Account { fallback: None } => {
+                ctx.resolve(self.identifier.as_deref()).await.to_string()
+            }
+        }
+    }
+}
+
 async fn prepare(
     ctx: &Ctx,
     router: &HttpRouter,
@@ -899,7 +1005,7 @@ async fn prepare(
     head: &mut Head,
     body_cap: usize,
     body_idle: Duration,
-) -> Result<Option<(Option<Vec<u8>>, String)>> {
+) -> Result<Option<Prepared>> {
     let idx = match router.match_index(head) {
         Some(i) => i,
         None => return Ok(None),
@@ -915,21 +1021,22 @@ async fn prepare(
         None
     };
 
-    let dest_id = match router.route_at(idx, head, body.as_deref()) {
+    let (target, identifier) = match router.route_at(idx, head, body.as_deref()) {
-        RouteOutcome::Pin { dest_id } => dest_id,
+        RouteOutcome::Pin { dest_id } => (Target::Pinned(dest_id), None),
         RouteOutcome::Identifier {
             identifier,
             fallback,
-        } => {
+        } => (
-            if identifier.is_none() && fallback.is_none() {
+            Target::Account { fallback },
-                ctx.resolve(None).await.to_string()
+            ctx.routing_identifier(identifier),
-            } else {
+        ),
-                ctx.resolve(identifier.as_deref()).await.to_string()
-            }
-        }
     };
 
-    Ok(Some((body, dest_id)))
+    Ok(Some(Prepared {
+        body,
+        target,
+        identifier,
+    }))
 }
 
 fn reason(status: u16) -> &'static str {

src/http/router.rs

@@ -4,9 +4,10 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
+use std::sync::Arc;
 use std::time::Duration;
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use globset::{Glob, GlobSet, GlobSetBuilder};
 use regex::Regex;
 
@@ -21,7 +22,7 @@ pub enum RouteOutcome {
     },
     Identifier {
         identifier: Option<String>,
-        fallback: Option<String>,
+        fallback: Option<Arc<str>>,
     },
 }
 
@@ -35,7 +36,7 @@ struct CompiledExtract {
 struct CompiledRoute {
     destination: Option<String>,
     extract: Option<CompiledExtract>,
-    fallback: Option<String>,
+    fallback: Option<Arc<str>>,
     needs_body: bool,
 }
 
@@ -144,8 +145,7 @@ impl HttpRouter {
         let value = head.header("authorization")?;
         let value = value.trim();
         if let Some(rest) = strip_scheme(value, "basic") {
-            let decoded = BASE64.decode(rest.trim()).ok()?;
+            let text = BASE64.decode_to_string(rest.trim()).ok()?;
-            let text = String::from_utf8(decoded).ok()?;
             let login = match text.split_once(':') {
                 Some((login, _)) => login,
                 None => text.as_str(),
@@ -186,7 +186,7 @@ fn compile_route(route: &HttpRoute) -> Result<CompiledRoute> {
     Ok(CompiledRoute {
         destination: route.destination.clone(),
         extract,
-        fallback: route.fallback.clone(),
+        fallback: route.fallback.as_deref().map(Arc::from),
         needs_body,
     })
 }
@@ -320,7 +320,7 @@ destination = "legacy"
 [[route]]
 match = "/**"
 extract = { from = "authorization" }
-fallback = "default"
+fallback = "legacy"
 "#,
         );
         let head = parse(b"GET /static HTTP/1.1\r\nHost: x\r\n\r\n");
@@ -331,7 +331,7 @@ fallback = "default"
         let head = parse(b"GET /dyn HTTP/1.1\r\nHost: x\r\n\r\n");
         match route(&router, &head, None) {
             RouteOutcome::Identifier { fallback, .. } => {
-                assert_eq!(fallback.as_deref(), Some("default"));
+                assert_eq!(fallback.as_deref(), Some("legacy"));
             }
             _ => panic!("expected identifier"),
         }
@@ -359,7 +359,7 @@ extract = { from = "authorization" }
 
     #[test]
     fn bearer_uses_bearer_identifier() {
-        use base64::engine::general_purpose::URL_SAFE_NO_PAD;
+        use encodify::base64::URL_SAFE_NO_PAD;
         let router = router_from_toml(
             r#"
 [[route]]

src/outbound.rs

@@ -190,7 +190,7 @@ pub async fn write_all(stream: &mut BoxedStream, bytes: &[u8]) -> Result<()> {
 
 const BRIDGE_BUF: usize = 16 * 1024;
 
-const SHUTDOWN_GRACE: Duration = Duration::from_secs(3);
+pub(crate) const SHUTDOWN_GRACE: Duration = Duration::from_secs(3);
 
 pub async fn bridge(
     mut client: BoxedStream,
@@ -245,7 +245,7 @@ pub async fn bridge(
     }
 }
 
-async fn wait_kick(cancel: Option<tokio::sync::watch::Receiver<bool>>) {
+pub(crate) async fn wait_kick(cancel: Option<tokio::sync::watch::Receiver<bool>>) {
     match cancel {
         Some(mut rx) => {
             while rx.changed().await.is_ok() {

src/proto/common.rs

@@ -23,7 +23,7 @@ use crate::error::{ProxyError, Result};
 use crate::imap_receiver::Mechanism;
 use crate::net::BoxedStream;
 use crate::net::tls;
-use crate::sasl::Credential;
+use crate::sasl::{Credential, SASL_RESPONSE};
 
 pub struct Handoff {
     pub stream: BoxedStream,
@@ -33,6 +33,22 @@ pub struct Handoff {
     pub residual: Vec<u8>,
 }
 
+pub struct Resume {
+    pub stream: BoxedStream,
+    pub buf: Vec<u8>,
+}
+
+pub fn take_rest(it: &mut std::slice::Iter<'_, u8>) -> Vec<u8> {
+    let rest = it.as_slice().to_vec();
+    *it = Default::default();
+    rest
+}
+
+pub fn bump(failures: &mut u32, max: u32) -> bool {
+    *failures += 1;
+    *failures >= max
+}
+
 pub fn credential_from_sasl(mech: &Mechanism, raw: &[u8]) -> Option<Credential> {
     match mech {
         Mechanism::Plain => Credential::decode_sasl_challenge_plain(raw),
@@ -117,13 +133,15 @@ pub fn sasl_cancelled(response: &[u8]) -> bool {
 }
 
 pub fn login_challenge(username_b64: &[u8], password_b64: &[u8]) -> Option<Vec<u8>> {
-    let username = crate::sasl::decode_sasl_ir(username_b64)?;
+    let mut raw = Vec::with_capacity(
-    let password = crate::sasl::decode_sasl_ir(password_b64)?;
+        SASL_RESPONSE.decoded_len_estimate(username_b64.len())
-    let mut raw = Vec::with_capacity(username.len() + password.len() + 2);
+            + SASL_RESPONSE.decoded_len_estimate(password_b64.len())
+            + 2,
+    );
     raw.push(0);
-    raw.extend_from_slice(&username);
+    SASL_RESPONSE.decode_append(username_b64, &mut raw).ok()?;
     raw.push(0);
-    raw.extend_from_slice(&password);
+    SASL_RESPONSE.decode_append(password_b64, &mut raw).ok()?;
     Some(raw)
 }
 
@@ -277,16 +295,22 @@ pub struct HealthSnapshot {
 }
 
 const REGISTRY_SHARDS: usize = 32;
+const MAX_LOGIN_HOLD: Duration = Duration::from_secs(120);
 
 struct LiveConn {
     id: u64,
     cancel: tokio::sync::watch::Sender<bool>,
 }
 
+struct LoginDelay {
+    until: Instant,
+    changed: tokio::sync::watch::Sender<()>,
+}
+
 #[derive(Default)]
 struct Shard {
     live: HashMap<Arc<str>, Vec<LiveConn>>,
-    delays: HashMap<Arc<str>, Instant>,
+    delays: HashMap<Arc<str>, LoginDelay>,
 }
 
 #[derive(Clone)]
@@ -326,9 +350,27 @@ impl ConnRegistry {
     }
 
     pub fn register(&self, identifier: &str) -> ConnGuard {
+        let (cancel, rx) = tokio::sync::watch::channel(false);
+        self.insert(identifier, cancel, rx)
+    }
+
+    pub fn register_cancel(
+        &self,
+        identifier: &str,
+        cancel: tokio::sync::watch::Sender<bool>,
+    ) -> ConnGuard {
+        let rx = cancel.subscribe();
+        self.insert(identifier, cancel, rx)
+    }
+
+    fn insert(
+        &self,
+        identifier: &str,
+        cancel: tokio::sync::watch::Sender<bool>,
+        rx: tokio::sync::watch::Receiver<bool>,
+    ) -> ConnGuard {
         static SEQ: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
         let id = SEQ.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
-        let (cancel, rx) = tokio::sync::watch::channel(false);
         let key: Arc<str> = Arc::from(identifier);
         let shard_idx = self.shard_idx(&key);
         self.shards[shard_idx]
@@ -362,21 +404,64 @@ impl ConnRegistry {
     pub fn set_delay(&self, identifier: &str, until: Instant) {
         let mut shard = self.shards[self.shard_idx(identifier)].lock();
         let now = Instant::now();
-        shard.delays.retain(|_, &mut u| u > now);
+        shard.delays.retain(|_, delay| delay.until > now);
-        shard.delays.insert(Arc::from(identifier), until);
+        match shard.delays.get_mut(identifier) {
+            Some(delay) => {
+                delay.until = until;
+                delay.changed.send_replace(());
+            }
+            None => {
+                shard.delays.insert(
+                    Arc::from(identifier),
+                    LoginDelay {
+                        until,
+                        changed: tokio::sync::watch::Sender::new(()),
+                    },
+                );
+            }
+        }
     }
 
-    pub fn delay_remaining(&self, identifier: &str) -> Option<Duration> {
+    fn delay(&self, identifier: &str) -> Option<(Instant, tokio::sync::watch::Receiver<()>)> {
         let mut shard = self.shards[self.shard_idx(identifier)].lock();
-        if let Some(&until) = shard.delays.get(identifier) {
+        let delay = shard.delays.get(identifier)?;
-            let now = Instant::now();
+        if Instant::now() < delay.until {
-            if now < until {
+            return Some((delay.until, delay.changed.subscribe()));
-                return Some(until - now);
-            }
-            shard.delays.remove(identifier);
         }
+        shard.delays.remove(identifier);
         None
     }
+
+    pub fn release_delay(&self, identifier: &str) {
+        self.shards[self.shard_idx(identifier)]
+            .lock()
+            .delays
+            .remove(identifier);
+    }
+
+    pub fn release_all_delays(&self) {
+        for shard in self.shards.iter() {
+            shard.lock().delays.clear();
+        }
+    }
+
+    pub async fn hold_login(&self, identifier: &str) {
+        let deadline = Instant::now() + MAX_LOGIN_HOLD;
+        while let Some((until, mut changed)) = self.delay(identifier) {
+            let wake = until.min(deadline);
+            if Instant::now() >= wake {
+                break;
+            }
+            tracing::debug!(
+                hold_ms = wake.saturating_duration_since(Instant::now()).as_millis() as u64,
+                "holding login (delay_until)"
+            );
+            tokio::select! {
+                _ = tokio::time::sleep_until(wake.into()) => {}
+                _ = changed.changed() => {}
+            }
+        }
+    }
 }
 
 impl ConnGuard {
@@ -509,15 +594,29 @@ impl Ctx {
         self.router.resolve(identifier).await
     }
 
+    pub async fn resolve_or(&self, identifier: Option<&str>, default: &Arc<str>) -> Arc<str> {
+        self.router.resolve_or(identifier, default).await
+    }
+
     pub fn register_conn(&self, identifier: &str) -> ConnGuard {
         self.conns.register(&self.router.normalize(identifier))
     }
 
+    pub fn register_conn_cancel(
+        &self,
+        identifier: &str,
+        cancel: tokio::sync::watch::Sender<bool>,
+    ) -> ConnGuard {
+        self.conns
+            .register_cancel(&self.router.normalize(identifier), cancel)
+    }
+
     pub fn routing_identifier(&self, identifier: Option<String>) -> Option<String> {
-        identifier.map(|id| {
+        let mut id = identifier?;
-            crate::route::master_account(&id, &self.config.routing.master_user_separators)
+        let account =
-                .to_string()
+            crate::route::master_account(&id, &self.config.routing.master_user_separators);
-        })
+        id.truncate(account.len());
+        (!id.is_empty()).then_some(id)
     }
 
     pub fn hide_auth_errors(&self, dest_id: &str) -> bool {
@@ -611,15 +710,8 @@ where
 }
 
 pub async fn hold_login(ctx: &Ctx, identifier: Option<&str>) {
-    if let Some(id) = identifier
+    if let Some(id) = identifier {
-        && let Some(remaining) = ctx.conns.delay_remaining(&ctx.router.normalize(id))
+        ctx.conns.hold_login(&ctx.router.normalize(id)).await;
-    {
-        let capped = remaining.min(Duration::from_secs(120));
-        tracing::debug!(
-            hold_ms = capped.as_millis() as u64,
-            "holding login (delay_until)"
-        );
-        tokio::time::sleep(capped).await;
     }
 }
 
@@ -679,6 +771,16 @@ pub enum AuthWire {
     ManageSieve,
 }
 
+impl AuthWire {
+    fn logout(&self) -> &'static [u8] {
+        match self {
+            AuthWire::Imap { .. } => b"ZZ LOGOUT\r\n",
+            AuthWire::Pop3 | AuthWire::Smtp => b"QUIT\r\n",
+            AuthWire::ManageSieve => b"LOGOUT\r\n",
+        }
+    }
+}
+
 enum AuthLine {
     Continuation,
     Passthrough,
@@ -810,7 +912,7 @@ pub async fn bridge_authenticated<F, Fut>(
     mut stream: BoxedStream,
     peer: SocketAddr,
     identifier: Option<&str>,
-    client_residual: &[u8],
+    client_residual: Vec<u8>,
     started: Instant,
     label: &'static str,
     wire: AuthWire,
@@ -818,7 +920,7 @@ pub async fn bridge_authenticated<F, Fut>(
     unavailable: &[u8],
     max: usize,
     open: F,
-) -> Result<()>
+) -> Result<Option<Resume>>
 where
     F: FnMut() -> Fut,
     Fut: Future<Output = Result<BackendLeg>>,
@@ -832,7 +934,7 @@ where
             "rejecting login: routing identifier contains invalid characters"
         );
         let _ = write(&mut stream, unavailable).await;
-        return Ok(());
+        return Ok(None);
     }
 
     let BackendLeg {
@@ -844,10 +946,11 @@ where
         Err(e) => {
             tracing::warn!(error = %e, protocol = label, destination = %dest_id, "backend unavailable");
             let _ = write(&mut stream, unavailable).await;
-            return Ok(());
+            return Ok(None);
         }
     };
 
+    let logout = wire.logout();
     let (auth_frame, pending_response) = auth.wire(accepts_initial_response);
     crate::outbound::write_all(&mut backend, auth_frame).await?;
 
@@ -872,16 +975,26 @@ where
         }
     };
 
-    let guard = if auth_ok {
+    if !auth_ok {
-        identifier.map(|id| ctx.register_conn(id))
+        tracing::debug!(
-    } else {
+            protocol = label,
-        None
+            destination = %dest_id,
-    };
+            "backend rejected authentication; resuming pre-authentication dialogue"
+        );
+        let _ = crate::outbound::write_all(&mut backend, logout).await;
+        let _ = tokio::time::timeout(crate::outbound::SHUTDOWN_GRACE, backend.shutdown()).await;
+        return Ok(Some(Resume {
+            stream,
+            buf: client_residual,
+        }));
+    }
+
+    let guard = identifier.map(|id| ctx.register_conn(id));
     let cancel = guard.as_ref().map(|g| g.cancel());
     let (to_backend, to_client) = crate::outbound::bridge(
         stream,
         backend,
-        client_residual,
+        &client_residual,
         &backend_residual,
         ctx.config.server.bridge_idle,
         cancel,
@@ -895,7 +1008,7 @@ where
         secs = started.elapsed().as_secs_f64(),
         "session closed"
     );
-    Ok(())
+    Ok(None)
 }
 
 pub async fn write(stream: &mut BoxedStream, bytes: &[u8]) -> Result<()> {
@@ -1049,7 +1162,7 @@ mod tests {
 
     #[test]
     fn login_challenge_builds_a_plain_authentication_frame() {
-        use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+        use encodify::base64::STANDARD as BASE64;
         let user = BASE64.encode("user@example.com");
         let pass = BASE64.encode("secret");
         assert_eq!(
@@ -1300,14 +1413,86 @@ mod tests {
         assert_eq!(reg.kick("user@example.com"), 0);
     }
 
+    #[tokio::test]
+    async fn conn_registry_release_ends_hold() {
+        // releasing a delay wakes a held login immediately
+        let reg = ConnRegistry::default();
+        reg.set_delay("user@example.com", Instant::now() + Duration::from_secs(60));
+        let held = reg.clone();
+        let hold = tokio::spawn(async move { held.hold_login("user@example.com").await });
+        tokio::time::sleep(Duration::from_millis(50)).await;
+        assert!(!hold.is_finished());
+        reg.release_delay("user@example.com");
+        tokio::time::timeout(Duration::from_secs(2), hold)
+            .await
+            .expect("release did not end the hold")
+            .unwrap();
+        assert!(reg.delay("user@example.com").is_none());
+    }
+
+    #[tokio::test]
+    async fn conn_registry_release_all_ends_holds() {
+        // releasing every delay wakes all held logins
+        let reg = ConnRegistry::default();
+        let until = Instant::now() + Duration::from_secs(60);
+        reg.set_delay("a@example.com", until);
+        reg.set_delay("b@example.com", until);
+        let holds = ["a@example.com", "b@example.com"].map(|id| {
+            let held = reg.clone();
+            tokio::spawn(async move { held.hold_login(id).await })
+        });
+        tokio::time::sleep(Duration::from_millis(50)).await;
+        reg.release_all_delays();
+        for hold in holds {
+            tokio::time::timeout(Duration::from_secs(2), hold)
+                .await
+                .expect("release did not end the hold")
+                .unwrap();
+        }
+    }
+
+    #[tokio::test]
+    async fn conn_registry_shortened_delay_ends_hold() {
+        // shortening a delay wakes a held login at the new deadline
+        let reg = ConnRegistry::default();
+        reg.set_delay("user@example.com", Instant::now() + Duration::from_secs(60));
+        let held = reg.clone();
+        let hold = tokio::spawn(async move { held.hold_login("user@example.com").await });
+        tokio::time::sleep(Duration::from_millis(50)).await;
+        reg.set_delay("user@example.com", Instant::now());
+        tokio::time::timeout(Duration::from_secs(2), hold)
+            .await
+            .expect("shortened delay did not end the hold")
+            .unwrap();
+    }
+
+    #[tokio::test]
+    async fn conn_registry_extended_delay_keeps_hold() {
+        // extending a delay keeps a held login waiting past the original deadline
+        let reg = ConnRegistry::default();
+        reg.set_delay(
+            "user@example.com",
+            Instant::now() + Duration::from_millis(100),
+        );
+        let held = reg.clone();
+        let started = Instant::now();
+        let hold = tokio::spawn(async move { held.hold_login("user@example.com").await });
+        reg.set_delay(
+            "user@example.com",
+            Instant::now() + Duration::from_millis(400),
+        );
+        hold.await.unwrap();
+        assert!(started.elapsed() >= Duration::from_millis(350));
+    }
+
     #[test]
     fn conn_registry_delay_window() {
         let reg = ConnRegistry::default();
-        assert!(reg.delay_remaining("user@example.com").is_none());
+        assert!(reg.delay("user@example.com").is_none());
         reg.set_delay("user@example.com", Instant::now() + Duration::from_secs(30));
-        assert!(reg.delay_remaining("user@example.com").is_some());
+        assert!(reg.delay("user@example.com").is_some());
         reg.set_delay("user@example.com", Instant::now());
-        assert!(reg.delay_remaining("user@example.com").is_none());
+        assert!(reg.delay("user@example.com").is_none());
     }
 
     #[test]

src/proto/imap.rs

@@ -6,7 +6,7 @@
 
 use std::net::SocketAddr;
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::AsyncReadExt;
 use tokio::time::timeout;
 
@@ -19,7 +19,7 @@ use crate::proto::common::{
     self, Ctx, assert_egress_encrypted, mechanism_name, plain_auth_allowed, read_crlf_line, write,
 };
 use crate::proto::forward;
-use crate::sasl::decode_sasl_ir;
+use crate::sasl::SASL_RESPONSE;
 use crate::token::identifier_from_credential;
 
 const MAX_PREAUTH: usize = 64 * 1024;
@@ -39,72 +39,101 @@ enum Decision {
 pub async fn handle(
     ctx: &Ctx,
     listener: &ListenerConfig,
-    stream: BoxedStream,
+    mut stream: BoxedStream,
     peer: SocketAddr,
     local: SocketAddr,
 ) -> Result<()> {
     let caps = &ctx.config.capabilities.imap;
+    let starttls_listener = listener.tls == TlsMode::Starttls;
 
-    let decision = match timeout(
+    let is_tls = stream.is_tls();
-        listener.preauth_timeout,
+    let greeting = format!(
-        preauth(ctx, listener, caps, stream),
+        "* OK [CAPABILITY {}] {}\r\n",
-    )
+        ctx.greetings.imap.get(is_tls, starttls_listener && !is_tls),
-    .await
+        caps.banner
-    {
-        Ok(Ok(d)) => d,
-        Ok(Err(e)) => return Err(e),
-        Err(_) => return Ok(()),
-    };
-
-    let Decision::Authenticate {
-        stream,
-        mech,
-        tag,
-        raw_challenge,
-        identifier,
-        residual,
-    } = decision
-    else {
-        return Ok(());
-    };
-
-    let identifier = ctx.routing_identifier(identifier);
-    let dest_id = ctx.resolve(identifier.as_deref()).await;
-    tracing::debug!(destination = %dest_id, "imap routing decision");
-
-    let started = std::time::Instant::now();
-    common::hold_login(ctx, identifier.as_deref()).await;
-
-    let client_tls = stream.is_tls();
-    let fwd = forward::ForwardInfo::new(peer, local, client_tls, None, ctx.config.server.proxy_ttl);
-
-    let mech_name = mechanism_name(&mech);
-    let response = BASE64.encode(&raw_challenge);
-    let auth = common::AuthFrame::inline(
-        format!("{tag} AUTHENTICATE {mech_name} {response}\r\n").into_bytes(),
-    )
-    .with_deferred(
-        format!("{tag} AUTHENTICATE {mech_name}\r\n").into_bytes(),
-        format!("{response}\r\n").into_bytes(),
     );
-    let unavailable = format!("{tag} NO [UNAVAILABLE] backend unavailable\r\n");
+    write(&mut stream, greeting.as_bytes()).await?;
 
-    common::bridge_authenticated(
+    let mut seed = Vec::new();
-        ctx,
+    let mut auth_failures = 0u32;
-        &dest_id,
+
-        stream,
+    loop {
-        peer,
+        let decision = match timeout(
-        identifier.as_deref(),
+            listener.preauth_timeout,
-        &residual,
+            preauth(ctx, listener, caps, stream, seed, &mut auth_failures),
-        started,
+        )
-        "imap",
+        .await
-        common::AuthWire::Imap { tag },
+        {
-        &auth,
+            Ok(Ok(d)) => d,
-        unavailable.as_bytes(),
+            Ok(Err(e)) => return Err(e),
-        MAX_PREAUTH,
+            Err(_) => return Ok(()),
-        || open_backend(ctx, &dest_id, &fwd),
+        };
-    )
+
-    .await
+        let Decision::Authenticate {
+            stream: client,
+            mech,
+            tag,
+            raw_challenge,
+            identifier,
+            residual,
+        } = decision
+        else {
+            return Ok(());
+        };
+
+        let identifier = ctx.routing_identifier(identifier);
+        let started = std::time::Instant::now();
+        common::hold_login(ctx, identifier.as_deref()).await;
+        let dest_id = ctx.resolve(identifier.as_deref()).await;
+        tracing::debug!(destination = %dest_id, "imap routing decision");
+
+        let client_tls = client.is_tls();
+        let fwd =
+            forward::ForwardInfo::new(peer, local, client_tls, None, ctx.config.server.proxy_ttl);
+
+        let mech_name = mechanism_name(&mech);
+        let mut response = String::with_capacity(BASE64.encoded_len(raw_challenge.len()) + 2);
+        BASE64.encode_append(&raw_challenge, &mut response);
+        response.push_str("\r\n");
+        let auth = common::AuthFrame::inline(
+            format!("{tag} AUTHENTICATE {mech_name} {response}").into_bytes(),
+        )
+        .with_deferred(
+            format!("{tag} AUTHENTICATE {mech_name}\r\n").into_bytes(),
+            response.into_bytes(),
+        );
+        let unavailable = format!("{tag} NO [UNAVAILABLE] backend unavailable\r\n");
+
+        let resume = common::bridge_authenticated(
+            ctx,
+            &dest_id,
+            client,
+            peer,
+            identifier.as_deref(),
+            residual,
+            started,
+            "imap",
+            common::AuthWire::Imap { tag },
+            &auth,
+            unavailable.as_bytes(),
+            MAX_PREAUTH,
+            || open_backend(ctx, &dest_id, &fwd),
+        )
+        .await?;
+
+        let Some(common::Resume {
+            stream: client,
+            buf,
+        }) = resume
+        else {
+            return Ok(());
+        };
+        if common::bump(&mut auth_failures, listener.max_auth_attempts) {
+            return Ok(());
+        }
+        stream = client;
+        seed = buf;
+    }
 }
 
 async fn preauth(
@@ -112,6 +141,8 @@ async fn preauth(
     listener: &ListenerConfig,
     caps: &ImapCapabilities,
     mut stream: BoxedStream,
+    seed: Vec<u8>,
+    auth_failures: &mut u32,
 ) -> Result<Decision> {
     let starttls_listener = listener.tls == TlsMode::Starttls;
     let mut auth = Auth {
@@ -119,31 +150,29 @@ async fn preauth(
         caps,
         is_tls: stream.is_tls(),
         max_attempts: listener.max_auth_attempts,
-        auth_failures: 0,
+        auth_failures,
     };
 
-    let greeting = format!(
-        "* OK [CAPABILITY {}] {}\r\n",
-        ctx.greetings
-            .imap
-            .get(auth.is_tls, starttls_listener && !auth.is_tls),
-        caps.banner
-    );
-    write(&mut stream, greeting.as_bytes()).await?;
-
     let mut receiver = Receiver::<Command>::new();
     receiver.max_request_size = MAX_PREAUTH;
     let mut read = [0u8; 8192];
+    let mut pending = seed;
 
     loop {
-        let n = stream
+        let chunk: &[u8] = if pending.is_empty() {
-            .read(&mut read)
+            let n = stream
-            .await
+                .read(&mut read)
-            .map_err(|e| ProxyError::Protocol(format!("reading client: {e}").into()))?;
+                .await
-        if n == 0 {
+                .map_err(|e| ProxyError::Protocol(format!("reading client: {e}").into()))?;
-            return Ok(Decision::Closed);
+            if n == 0 {
-        }
+                return Ok(Decision::Closed);
-        let mut it = read[..n].iter();
+            }
+            &read[..n]
+        } else {
+            &pending
+        };
+        let mut it = chunk.iter();
+        let mut carry: Option<Vec<u8>> = None;
 
         loop {
             match receiver.parse(&mut it) {
@@ -234,6 +263,10 @@ async fn preauth(
                                         residual,
                                     });
                                 }
+                                Step::Resume { residual } => {
+                                    carry = Some(residual);
+                                    break;
+                                }
                                 Step::Continue => {}
                                 Step::Close => return Ok(Decision::Closed),
                             }
@@ -255,6 +288,10 @@ async fn preauth(
                                         residual,
                                     });
                                 }
+                                Step::Resume { residual } => {
+                                    carry = Some(residual);
+                                    break;
+                                }
                                 Step::Continue => {}
                                 Step::Close => return Ok(Decision::Closed),
                             }
@@ -280,13 +317,17 @@ async fn preauth(
                 }
                 Err(RecvError::Parse { message }) => {
                     write(&mut stream, format!("* BAD {message}\r\n").as_bytes()).await?;
-                    auth.auth_failures += 1;
+                    if common::bump(auth.auth_failures, auth.max_attempts) {
-                    if auth.auth_failures >= auth.max_attempts {
                         return Ok(Decision::Closed);
                     }
                 }
             }
         }
+        drop(it);
+        match carry {
+            Some(rest) => pending = rest,
+            None => pending.clear(),
+        }
     }
 }
 
@@ -295,11 +336,14 @@ struct Auth<'a> {
     caps: &'a ImapCapabilities,
     is_tls: bool,
     max_attempts: u32,
-    auth_failures: u32,
+    auth_failures: &'a mut u32,
 }
 
 enum Step {
     Continue,
+    Resume {
+        residual: Vec<u8>,
+    },
     Close,
     Finalize {
         mech: Mechanism,
@@ -332,7 +376,7 @@ impl Auth<'_> {
             Mechanism::Login if common::sasl_offered(&self.caps.sasl, "LOGIN") => {}
             _ => {
                 return self
-                    .reject(stream, tag, "Unsupported authentication mechanism.")
+                    .reject(stream, tag, "Unsupported authentication mechanism.", None)
                     .await;
             }
         }
@@ -354,16 +398,21 @@ impl Auth<'_> {
         }
 
         let (raw_b64, residual): (Vec<u8>, Vec<u8>) = if let Some(ir) = tokens.get(1) {
-            (ir.as_bytes().to_vec(), it.as_slice().to_vec())
+            (ir.as_bytes().to_vec(), common::take_rest(it))
         } else {
             write(&mut *stream, b"+ \r\n").await?;
-            let seed = it.as_slice().to_vec();
+            let seed = common::take_rest(it);
             read_crlf_line(stream, seed, MAX_PREAUTH).await?
         };
 
-        let Some(raw) = decode_sasl_ir(&raw_b64) else {
+        let Ok(raw) = SASL_RESPONSE.decode(&raw_b64) else {
             return self
-                .reject(stream, tag, "Invalid base64 in SASL response.")
+                .reject(
+                    stream,
+                    tag,
+                    "Invalid base64 in SASL response.",
+                    Some(residual),
+                )
                 .await;
         };
 
@@ -378,18 +427,20 @@ impl Auth<'_> {
         it: &mut std::slice::Iter<'_, u8>,
     ) -> Result<Step> {
         let (user_b64, residual): (Vec<u8>, Vec<u8>) = if let Some(ir) = tokens.get(1) {
-            (ir.as_bytes().to_vec(), it.as_slice().to_vec())
+            (ir.as_bytes().to_vec(), common::take_rest(it))
         } else {
             write(
                 &mut *stream,
                 format!("+ {}\r\n", common::LOGIN_USERNAME_CHALLENGE).as_bytes(),
             )
             .await?;
-            let seed = it.as_slice().to_vec();
+            let seed = common::take_rest(it);
             read_crlf_line(stream, seed, MAX_PREAUTH).await?
         };
         if common::sasl_cancelled(&user_b64) {
-            return self.reject(stream, tag, "Authentication cancelled.").await;
+            return self
+                .reject(stream, tag, "Authentication cancelled.", Some(residual))
+                .await;
         }
 
         write(
@@ -399,12 +450,19 @@ impl Auth<'_> {
         .await?;
         let (pass_b64, residual) = read_crlf_line(stream, residual, MAX_PREAUTH).await?;
         if common::sasl_cancelled(&pass_b64) {
-            return self.reject(stream, tag, "Authentication cancelled.").await;
+            return self
+                .reject(stream, tag, "Authentication cancelled.", Some(residual))
+                .await;
         }
 
         let Some(raw) = common::login_challenge(&user_b64, &pass_b64) else {
             return self
-                .reject(stream, tag, "Invalid base64 in SASL response.")
+                .reject(
+                    stream,
+                    tag,
+                    "Invalid base64 in SASL response.",
+                    Some(residual),
+                )
                 .await;
         };
 
@@ -429,7 +487,7 @@ impl Auth<'_> {
         }
         let (Some(user), Some(pass)) = (tokens.first(), tokens.get(1)) else {
             return self
-                .reject(stream, tag, "LOGIN requires a username and password.")
+                .reject(stream, tag, "LOGIN requires a username and password.", None)
                 .await;
         };
         let (user, pass) = (user.as_bytes(), pass.as_bytes());
@@ -438,7 +496,7 @@ impl Auth<'_> {
         raw.extend_from_slice(user);
         raw.push(0);
         raw.extend_from_slice(pass);
-        let residual = it.as_slice().to_vec();
+        let residual = common::take_rest(it);
 
         self.finish(stream, Mechanism::Plain, tag, raw, residual)
             .await
@@ -453,7 +511,9 @@ impl Auth<'_> {
         residual: Vec<u8>,
     ) -> Result<Step> {
         let Some(cred) = common::credential_from_sasl(&mech, &raw) else {
-            return self.reject(stream, tag, "Malformed credentials.").await;
+            return self
+                .reject(stream, tag, "Malformed credentials.", Some(residual))
+                .await;
         };
         let identifier =
             identifier_from_credential(&cred, &self.ctx.config.oauth.jwt_username_claim);
@@ -466,14 +526,21 @@ impl Auth<'_> {
         })
     }
 
-    async fn reject(&mut self, stream: &mut BoxedStream, tag: &str, message: &str) -> Result<Step> {
+    async fn reject(
+        &mut self,
+        stream: &mut BoxedStream,
+        tag: &str,
+        message: &str,
+        residual: Option<Vec<u8>>,
+    ) -> Result<Step> {
         write(&mut *stream, format!("{tag} NO {message}\r\n").as_bytes()).await?;
-        self.auth_failures += 1;
+        if common::bump(self.auth_failures, self.max_attempts) {
-        if self.auth_failures >= self.max_attempts {
+            return Ok(Step::Close);
-            Ok(Step::Close)
-        } else {
-            Ok(Step::Continue)
         }
+        Ok(match residual {
+            Some(residual) => Step::Resume { residual },
+            None => Step::Continue,
+        })
     }
 }
 

src/proto/managesieve.rs

@@ -6,7 +6,7 @@
 
 use std::net::SocketAddr;
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::AsyncReadExt;
 use tokio::time::timeout;
 
@@ -16,11 +16,11 @@ use crate::imap_receiver::{Command, Error as RecvError, Mechanism, Receiver, Sta
 use crate::net::BoxedStream;
 use crate::outbound;
 use crate::proto::common::{
-    self, Ctx, Handoff, assert_egress_encrypted, credential_from_sasl, mechanism_name,
+    self, Ctx, Handoff, assert_egress_encrypted, bump, credential_from_sasl, mechanism_name,
     plain_auth_allowed, write,
 };
 use crate::proto::forward;
-use crate::sasl::decode_sasl_ir;
+use crate::sasl::SASL_RESPONSE;
 use crate::token::identifier_from_credential;
 
 const MAX_PREAUTH: usize = 64 * 1024;
@@ -28,80 +28,14 @@ const MAX_PREAUTH: usize = 64 * 1024;
 pub async fn handle(
     ctx: &Ctx,
     listener: &ListenerConfig,
-    stream: BoxedStream,
+    mut stream: BoxedStream,
     peer: SocketAddr,
     local: SocketAddr,
 ) -> Result<()> {
     let caps = &ctx.config.capabilities.managesieve;
-
-    let handoff = match timeout(
-        listener.preauth_timeout,
-        preauth(ctx, listener, caps, stream),
-    )
-    .await
-    {
-        Ok(Ok(Some(h))) => h,
-        Ok(Ok(None)) => return Ok(()),
-        Ok(Err(e)) => return Err(e),
-        Err(_) => return Ok(()),
-    };
-
-    let Handoff {
-        stream,
-        mech,
-        raw_challenge,
-        identifier,
-        residual,
-    } = handoff;
-
-    let identifier = ctx.routing_identifier(identifier);
-    let dest_id = ctx.resolve(identifier.as_deref()).await;
-    let started = std::time::Instant::now();
-    common::hold_login(ctx, identifier.as_deref()).await;
-    let fwd = forward::ForwardInfo::new(
-        peer,
-        local,
-        stream.is_tls(),
-        None,
-        ctx.config.server.proxy_ttl,
-    );
-
-    let auth = common::AuthFrame::inline(
-        format!(
-            "AUTHENTICATE \"{}\" \"{}\"\r\n",
-            mechanism_name(&mech),
-            BASE64.encode(&raw_challenge)
-        )
-        .into_bytes(),
-    );
-
-    common::bridge_authenticated(
-        ctx,
-        &dest_id,
-        stream,
-        peer,
-        identifier.as_deref(),
-        &residual,
-        started,
-        "managesieve",
-        common::AuthWire::ManageSieve,
-        &auth,
-        b"NO \"backend unavailable\"\r\n",
-        MAX_PREAUTH,
-        || open_backend(ctx, &dest_id, &fwd),
-    )
-    .await
-}
-
-async fn preauth(
-    ctx: &Ctx,
-    listener: &ListenerConfig,
-    caps: &ManageSieveCapabilities,
-    mut stream: BoxedStream,
-) -> Result<Option<Handoff>> {
-    let mut is_tls = stream.is_tls();
     let starttls_listener = listener.tls == TlsMode::Starttls;
 
+    let is_tls = stream.is_tls();
     write(
         &mut stream,
         ctx.greetings
@@ -111,21 +45,111 @@ async fn preauth(
     )
     .await?;
 
+    let mut seed = Vec::new();
+    let mut auth_failures = 0u32;
+
+    loop {
+        let handoff = match timeout(
+            listener.preauth_timeout,
+            preauth(ctx, listener, caps, stream, seed, &mut auth_failures),
+        )
+        .await
+        {
+            Ok(Ok(Some(h))) => h,
+            Ok(Ok(None)) => return Ok(()),
+            Ok(Err(e)) => return Err(e),
+            Err(_) => return Ok(()),
+        };
+
+        let Handoff {
+            stream: client,
+            mech,
+            raw_challenge,
+            identifier,
+            residual,
+        } = handoff;
+
+        let identifier = ctx.routing_identifier(identifier);
+        let started = std::time::Instant::now();
+        common::hold_login(ctx, identifier.as_deref()).await;
+        let dest_id = ctx.resolve(identifier.as_deref()).await;
+        let fwd = forward::ForwardInfo::new(
+            peer,
+            local,
+            client.is_tls(),
+            None,
+            ctx.config.server.proxy_ttl,
+        );
+
+        let mut frame = format!("AUTHENTICATE \"{}\" \"", mechanism_name(&mech));
+        BASE64.encode_append(&raw_challenge, &mut frame);
+        frame.push_str("\"\r\n");
+        let auth = common::AuthFrame::inline(frame.into_bytes());
+
+        let resume = common::bridge_authenticated(
+            ctx,
+            &dest_id,
+            client,
+            peer,
+            identifier.as_deref(),
+            residual,
+            started,
+            "managesieve",
+            common::AuthWire::ManageSieve,
+            &auth,
+            b"NO \"backend unavailable\"\r\n",
+            MAX_PREAUTH,
+            || open_backend(ctx, &dest_id, &fwd),
+        )
+        .await?;
+
+        let Some(common::Resume {
+            stream: client,
+            buf,
+        }) = resume
+        else {
+            return Ok(());
+        };
+        if bump(&mut auth_failures, listener.max_auth_attempts) {
+            return Ok(());
+        }
+        stream = client;
+        seed = buf;
+    }
+}
+
+async fn preauth(
+    ctx: &Ctx,
+    listener: &ListenerConfig,
+    caps: &ManageSieveCapabilities,
+    mut stream: BoxedStream,
+    seed: Vec<u8>,
+    auth_failures: &mut u32,
+) -> Result<Option<Handoff>> {
+    let mut is_tls = stream.is_tls();
+    let starttls_listener = listener.tls == TlsMode::Starttls;
+
     let mut receiver =
         Receiver::<Command>::new().with_start_state(State::Command { is_uid: false });
     receiver.max_request_size = MAX_PREAUTH;
-    let mut auth_failures = 0u32;
     let mut read = [0u8; 8192];
+    let mut pending = seed;
 
     loop {
-        let n = stream
+        let chunk: &[u8] = if pending.is_empty() {
-            .read(&mut read)
+            let n = stream
-            .await
+                .read(&mut read)
-            .map_err(|e| ProxyError::Protocol(format!("reading client: {e}").into()))?;
+                .await
-        if n == 0 {
+                .map_err(|e| ProxyError::Protocol(format!("reading client: {e}").into()))?;
-            return Ok(None);
+            if n == 0 {
-        }
+                return Ok(None);
-        let mut it = read[..n].iter();
+            }
+            &read[..n]
+        } else {
+            &pending
+        };
+        let mut it = chunk.iter();
+        let mut carry: Option<Vec<u8>> = None;
 
         loop {
             match receiver.parse(&mut it) {
@@ -179,7 +203,7 @@ async fn preauth(
                                 common::sasl_offered(&caps.sasl, "LOGIN"),
                                 &req.tokens,
                                 &mut it,
-                                &mut auth_failures,
+                                &mut *auth_failures,
                                 listener.max_auth_attempts,
                             )
                             .await?
@@ -198,6 +222,10 @@ async fn preauth(
                                         residual,
                                     }));
                                 }
+                                AuthStep::Resume { residual } => {
+                                    carry = Some(residual);
+                                    break;
+                                }
                                 AuthStep::Continue => {}
                                 AuthStep::Close => return Ok(None),
                             }
@@ -222,13 +250,17 @@ async fn preauth(
                         format!("NO \"{}\"\r\n", sanitize(&message)).as_bytes(),
                     )
                     .await?;
-                    auth_failures += 1;
+                    if bump(auth_failures, listener.max_auth_attempts) {
-                    if auth_failures >= listener.max_auth_attempts {
                         return Ok(None);
                     }
                 }
             }
         }
+        drop(it);
+        match carry {
+            Some(rest) => pending = rest,
+            None => pending.clear(),
+        }
     }
 }
 
@@ -240,6 +272,9 @@ enum AuthStep {
         residual: Vec<u8>,
     },
     Continue,
+    Resume {
+        residual: Vec<u8>,
+    },
     Close,
 }
 
@@ -262,7 +297,16 @@ async fn handle_authenticate(
     match mech {
         Mechanism::Plain | Mechanism::OAuthBearer | Mechanism::XOauth2 => {}
         Mechanism::Login if login_offered => {}
-        _ => return fail(stream, "Unsupported mechanism", auth_failures, max_attempts).await,
+        _ => {
+            return fail(
+                stream,
+                "Unsupported mechanism",
+                auth_failures,
+                max_attempts,
+                None,
+            )
+            .await;
+        }
     }
     if matches!(mech, Mechanism::Plain | Mechanism::Login) && !plain_ok {
         write(
@@ -278,18 +322,32 @@ async fn handle_authenticate(
     }
 
     let (raw_b64, residual): (Vec<u8>, Vec<u8>) = if let Some(ir) = tokens.get(1) {
-        (ir.as_bytes().to_vec(), it.as_slice().to_vec())
+        (ir.as_bytes().to_vec(), common::take_rest(it))
     } else {
         write(&mut *stream, b"{0}\r\n").await?;
-        let seed = it.as_slice().to_vec();
+        let seed = common::take_rest(it);
         read_sasl_response(stream, seed).await?
     };
 
-    let Some(raw) = decode_sasl_ir(&raw_b64) else {
+    let Ok(raw) = SASL_RESPONSE.decode(&raw_b64) else {
-        return fail(stream, "Invalid base64", auth_failures, max_attempts).await;
+        return fail(
+            stream,
+            "Invalid base64",
+            auth_failures,
+            max_attempts,
+            Some(residual),
+        )
+        .await;
     };
     let Some(cred) = credential_from_sasl(&mech, &raw) else {
-        return fail(stream, "Malformed credentials", auth_failures, max_attempts).await;
+        return fail(
+            stream,
+            "Malformed credentials",
+            auth_failures,
+            max_attempts,
+            Some(residual),
+        )
+        .await;
     };
     let identifier = identifier_from_credential(&cred, &ctx.config.oauth.jwt_username_claim);
 
@@ -310,10 +368,10 @@ async fn authenticate_login(
     max_attempts: u32,
 ) -> Result<AuthStep> {
     let (user_b64, residual): (Vec<u8>, Vec<u8>) = if let Some(ir) = tokens.get(1) {
-        (ir.as_bytes().to_vec(), it.as_slice().to_vec())
+        (ir.as_bytes().to_vec(), common::take_rest(it))
     } else {
         write_challenge(stream, common::LOGIN_USERNAME_CHALLENGE).await?;
-        let seed = it.as_slice().to_vec();
+        let seed = common::take_rest(it);
         read_sasl_response(stream, seed).await?
     };
     if common::sasl_cancelled(&user_b64) {
@@ -322,6 +380,7 @@ async fn authenticate_login(
             "Authentication cancelled",
             auth_failures,
             max_attempts,
+            Some(residual),
         )
         .await;
     }
@@ -334,15 +393,30 @@ async fn authenticate_login(
             "Authentication cancelled",
             auth_failures,
             max_attempts,
+            Some(residual),
         )
         .await;
     }
 
     let Some(raw) = common::login_challenge(&user_b64, &pass_b64) else {
-        return fail(stream, "Invalid base64", auth_failures, max_attempts).await;
+        return fail(
+            stream,
+            "Invalid base64",
+            auth_failures,
+            max_attempts,
+            Some(residual),
+        )
+        .await;
     };
     let Some(cred) = credential_from_sasl(&Mechanism::Plain, &raw) else {
-        return fail(stream, "Malformed credentials", auth_failures, max_attempts).await;
+        return fail(
+            stream,
+            "Malformed credentials",
+            auth_failures,
+            max_attempts,
+            Some(residual),
+        )
+        .await;
     };
     let identifier = identifier_from_credential(&cred, &ctx.config.oauth.jwt_username_claim);
 
@@ -367,14 +441,16 @@ async fn fail(
     message: &str,
     auth_failures: &mut u32,
     max_attempts: u32,
+    residual: Option<Vec<u8>>,
 ) -> Result<AuthStep> {
     write(&mut *stream, format!("NO \"{message}\"\r\n").as_bytes()).await?;
-    *auth_failures += 1;
+    if bump(auth_failures, max_attempts) {
-    if *auth_failures >= max_attempts {
+        return Ok(AuthStep::Close);
-        Ok(AuthStep::Close)
-    } else {
-        Ok(AuthStep::Continue)
     }
+    Ok(match residual {
+        Some(residual) => AuthStep::Resume { residual },
+        None => AuthStep::Continue,
+    })
 }
 
 async fn read_sasl_response(stream: &mut BoxedStream, seed: Vec<u8>) -> Result<(Vec<u8>, Vec<u8>)> {

src/proto/pop3.rs

@@ -6,7 +6,7 @@
 
 use std::net::SocketAddr;
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::time::timeout;
 
 use crate::config::{Forwarding, ListenerConfig, Pop3Capabilities, Protocol, TlsMode};
@@ -15,11 +15,11 @@ use crate::imap_receiver::Mechanism;
 use crate::net::BoxedStream;
 use crate::outbound;
 use crate::proto::common::{
-    self, Ctx, Handoff, assert_egress_encrypted, credential_from_sasl, mechanism_name,
+    self, Ctx, Handoff, assert_egress_encrypted, bump, credential_from_sasl, mechanism_name,
     plain_auth_allowed, write,
 };
 use crate::proto::forward;
-use crate::sasl::decode_sasl_ir;
+use crate::sasl::SASL_RESPONSE;
 use crate::token::identifier_from_credential;
 
 const MAX_PREAUTH: usize = 64 * 1024;
@@ -27,69 +27,85 @@ const MAX_PREAUTH: usize = 64 * 1024;
 pub async fn handle(
     ctx: &Ctx,
     listener: &ListenerConfig,
-    stream: BoxedStream,
+    mut stream: BoxedStream,
     peer: SocketAddr,
     local: SocketAddr,
 ) -> Result<()> {
     let caps = &ctx.config.capabilities.pop3;
 
-    let handoff = match timeout(
+    write(&mut stream, format!("+OK {}\r\n", caps.banner).as_bytes()).await?;
-        listener.preauth_timeout,
-        preauth(ctx, listener, caps, stream),
-    )
-    .await
-    {
-        Ok(Ok(Some(h))) => h,
-        Ok(Ok(None)) => return Ok(()),
-        Ok(Err(e)) => return Err(e),
-        Err(_) => return Ok(()),
-    };
 
-    let Handoff {
+    let mut seed = Vec::with_capacity(1024);
-        stream,
+    let mut auth_failures = 0u32;
-        mech,
-        raw_challenge,
-        identifier,
-        residual,
-    } = handoff;
 
-    let identifier = ctx.routing_identifier(identifier);
+    loop {
-    let dest_id = ctx.resolve(identifier.as_deref()).await;
+        let handoff = match timeout(
-    let started = std::time::Instant::now();
+            listener.preauth_timeout,
-    common::hold_login(ctx, identifier.as_deref()).await;
+            preauth(ctx, listener, caps, stream, seed, &mut auth_failures),
-    let fwd = forward::ForwardInfo::new(
-        peer,
-        local,
-        stream.is_tls(),
-        None,
-        ctx.config.server.proxy_ttl,
-    );
-
-    let auth = common::AuthFrame::inline(
-        format!(
-            "AUTH {} {}\r\n",
-            mechanism_name(&mech),
-            BASE64.encode(&raw_challenge)
         )
-        .into_bytes(),
+        .await
-    );
+        {
+            Ok(Ok(Some(h))) => h,
+            Ok(Ok(None)) => return Ok(()),
+            Ok(Err(e)) => return Err(e),
+            Err(_) => return Ok(()),
+        };
 
-    common::bridge_authenticated(
+        let Handoff {
-        ctx,
+            stream: client,
-        &dest_id,
+            mech,
-        stream,
+            raw_challenge,
-        peer,
+            identifier,
-        identifier.as_deref(),
+            residual,
-        &residual,
+        } = handoff;
-        started,
+
-        "pop3",
+        let identifier = ctx.routing_identifier(identifier);
-        common::AuthWire::Pop3,
+        let started = std::time::Instant::now();
-        &auth,
+        common::hold_login(ctx, identifier.as_deref()).await;
-        b"-ERR backend unavailable\r\n",
+        let dest_id = ctx.resolve(identifier.as_deref()).await;
-        MAX_PREAUTH,
+        let fwd = forward::ForwardInfo::new(
-        || open_backend(ctx, &dest_id, &fwd),
+            peer,
-    )
+            local,
-    .await
+            client.is_tls(),
+            None,
+            ctx.config.server.proxy_ttl,
+        );
+
+        let mut frame = format!("AUTH {} ", mechanism_name(&mech));
+        BASE64.encode_append(&raw_challenge, &mut frame);
+        frame.push_str("\r\n");
+        let auth = common::AuthFrame::inline(frame.into_bytes());
+
+        let resume = common::bridge_authenticated(
+            ctx,
+            &dest_id,
+            client,
+            peer,
+            identifier.as_deref(),
+            residual,
+            started,
+            "pop3",
+            common::AuthWire::Pop3,
+            &auth,
+            b"-ERR backend unavailable\r\n",
+            MAX_PREAUTH,
+            || open_backend(ctx, &dest_id, &fwd),
+        )
+        .await?;
+
+        let Some(common::Resume {
+            stream: client,
+            buf,
+        }) = resume
+        else {
+            return Ok(());
+        };
+        if bump(&mut auth_failures, listener.max_auth_attempts) {
+            return Ok(());
+        }
+        stream = client;
+        seed = buf;
+    }
 }
 
 async fn preauth(
@@ -97,15 +113,14 @@ async fn preauth(
     listener: &ListenerConfig,
     caps: &Pop3Capabilities,
     mut stream: BoxedStream,
+    seed: Vec<u8>,
+    auth_failures: &mut u32,
 ) -> Result<Option<Handoff>> {
     let mut is_tls = stream.is_tls();
     let starttls_listener = listener.tls == TlsMode::Starttls;
 
-    write(&mut stream, format!("+OK {}\r\n", caps.banner).as_bytes()).await?;
+    let mut buf: Vec<u8> = seed;
-
-    let mut buf: Vec<u8> = Vec::with_capacity(1024);
     let mut pending_user: Option<Vec<u8>> = None;
-    let mut auth_failures = 0u32;
 
     loop {
         let Some(nl) = buf.iter().position(|&b| b == b'\n') else {
@@ -227,7 +242,7 @@ async fn preauth(
                     _ => {
                         write(&mut stream, b"-ERR unsupported mechanism\r\n").await?;
                         buf.drain(..consumed);
-                        if bump(&mut auth_failures, listener.max_auth_attempts) {
+                        if bump(auth_failures, listener.max_auth_attempts) {
                             return Ok(None);
                         }
                         continue;
@@ -259,7 +274,7 @@ async fn preauth(
                     if common::sasl_cancelled(&user_b64) {
                         buf = rest;
                         write(&mut stream, b"-ERR authentication cancelled\r\n").await?;
-                        if bump(&mut auth_failures, listener.max_auth_attempts) {
+                        if bump(auth_failures, listener.max_auth_attempts) {
                             return Ok(None);
                         }
                         continue;
@@ -274,21 +289,21 @@ async fn preauth(
                     buf = rest;
                     if common::sasl_cancelled(&pass_b64) {
                         write(&mut stream, b"-ERR authentication cancelled\r\n").await?;
-                        if bump(&mut auth_failures, listener.max_auth_attempts) {
+                        if bump(auth_failures, listener.max_auth_attempts) {
                             return Ok(None);
                         }
                         continue;
                     }
                     let Some(raw) = common::login_challenge(&user_b64, &pass_b64) else {
                         write(&mut stream, b"-ERR invalid base64\r\n").await?;
-                        if bump(&mut auth_failures, listener.max_auth_attempts) {
+                        if bump(auth_failures, listener.max_auth_attempts) {
                             return Ok(None);
                         }
                         continue;
                     };
                     let Some(cred) = credential_from_sasl(&Mechanism::Plain, &raw) else {
                         write(&mut stream, b"-ERR malformed credentials\r\n").await?;
-                        if bump(&mut auth_failures, listener.max_auth_attempts) {
+                        if bump(auth_failures, listener.max_auth_attempts) {
                             return Ok(None);
                         }
                         continue;
@@ -319,16 +334,16 @@ async fn preauth(
                     line
                 };
 
-                let Some(raw) = decode_sasl_ir(&raw_b64) else {
+                let Ok(raw) = SASL_RESPONSE.decode(&raw_b64) else {
                     write(&mut stream, b"-ERR invalid base64\r\n").await?;
-                    if bump(&mut auth_failures, listener.max_auth_attempts) {
+                    if bump(auth_failures, listener.max_auth_attempts) {
                         return Ok(None);
                     }
                     continue;
                 };
                 let Some(cred) = credential_from_sasl(&mech, &raw) else {
                     write(&mut stream, b"-ERR malformed credentials\r\n").await?;
-                    if bump(&mut auth_failures, listener.max_auth_attempts) {
+                    if bump(auth_failures, listener.max_auth_attempts) {
                         return Ok(None);
                     }
                     continue;
@@ -352,11 +367,6 @@ async fn preauth(
     }
 }
 
-fn bump(failures: &mut u32, max: u32) -> bool {
-    *failures += 1;
-    *failures >= max
-}
-
 fn split_verb(line: &[u8]) -> (&[u8], &[u8]) {
     match line.iter().position(|&b| b == b' ') {
         Some(pos) => (&line[..pos], trim_leading_space(&line[pos + 1..])),

src/proto/smtp.rs

@@ -6,7 +6,7 @@
 
 use std::net::SocketAddr;
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use smtp_proto::{
     AUTH_LOGIN, AUTH_OAUTHBEARER, AUTH_PLAIN, AUTH_XOAUTH2, Error as SmtpError, Request,
 };
@@ -18,11 +18,11 @@ use crate::imap_receiver::Mechanism;
 use crate::net::BoxedStream;
 use crate::outbound;
 use crate::proto::common::{
-    self, Ctx, Handoff, assert_egress_encrypted, credential_from_sasl, mechanism_name,
+    self, Ctx, Handoff, assert_egress_encrypted, bump, credential_from_sasl, mechanism_name,
     plain_auth_allowed, write,
 };
 use crate::proto::forward;
-use crate::sasl::decode_sasl_ir;
+use crate::sasl::SASL_RESPONSE;
 use crate::token::identifier_from_credential;
 
 const MAX_PREAUTH: usize = 64 * 1024;
@@ -32,73 +32,112 @@ struct SubmissionHandoff {
     ehlo_host: String,
 }
 
+struct SubmissionState {
+    buf: Vec<u8>,
+    auth_failures: u32,
+    ehlo_host: String,
+}
+
+impl Default for SubmissionState {
+    fn default() -> Self {
+        SubmissionState {
+            buf: Vec::with_capacity(1024),
+            auth_failures: 0,
+            ehlo_host: String::new(),
+        }
+    }
+}
+
 pub async fn handle_submission(
     ctx: &Ctx,
     listener: &ListenerConfig,
-    stream: BoxedStream,
+    mut stream: BoxedStream,
     peer: SocketAddr,
     local: SocketAddr,
 ) -> Result<()> {
     let caps = &ctx.config.capabilities.submission;
 
-    let sh = match timeout(
+    let hostname = ctx.config.server.hostname_for(local);
-        listener.preauth_timeout,
+    write(
-        preauth(ctx, listener, caps, stream, local),
+        &mut stream,
+        format!("220 {hostname} ESMTP {}\r\n", caps.banner).as_bytes(),
     )
-    .await
+    .await?;
-    {
-        Ok(Ok(Some(h))) => h,
-        Ok(Ok(None)) => return Ok(()),
-        Ok(Err(e)) => return Err(e),
-        Err(_) => return Ok(()),
-    };
 
-    let SubmissionHandoff { handoff, ehlo_host } = sh;
+    let mut state = SubmissionState::default();
-    let Handoff {
-        stream,
-        mech,
-        raw_challenge,
-        identifier,
-        residual,
-    } = handoff;
 
-    let identifier = ctx.routing_identifier(identifier);
+    loop {
-    let dest_id = ctx.resolve(identifier.as_deref()).await;
+        let sh = match timeout(
-    let started = std::time::Instant::now();
+            listener.preauth_timeout,
-    common::hold_login(ctx, identifier.as_deref()).await;
+            preauth(ctx, listener, caps, stream, &hostname, &mut state),
-    let fwd = forward::ForwardInfo::new(
-        peer,
-        local,
-        stream.is_tls(),
-        Some(ehlo_host),
-        ctx.config.server.proxy_ttl,
-    );
-
-    let auth = common::AuthFrame::inline(
-        format!(
-            "AUTH {} {}\r\n",
-            mechanism_name(&mech),
-            BASE64.encode(&raw_challenge)
         )
-        .into_bytes(),
+        .await
-    );
+        {
+            Ok(Ok(Some(h))) => h,
+            Ok(Ok(None)) => return Ok(()),
+            Ok(Err(e)) => return Err(e),
+            Err(_) => return Ok(()),
+        };
 
-    common::bridge_authenticated(
+        let SubmissionHandoff {
-        ctx,
+            handoff,
-        &dest_id,
+            ehlo_host: announced,
-        stream,
+        } = sh;
-        peer,
+        let Handoff {
-        identifier.as_deref(),
+            stream: client,
-        &residual,
+            mech,
-        started,
+            raw_challenge,
-        "submission",
+            identifier,
-        common::AuthWire::Smtp,
+            residual,
-        &auth,
+        } = handoff;
-        b"421 4.3.0 backend unavailable\r\n",
+
-        MAX_PREAUTH,
+        let identifier = ctx.routing_identifier(identifier);
-        || open_backend(ctx, &dest_id, &fwd),
+        let started = std::time::Instant::now();
-    )
+        common::hold_login(ctx, identifier.as_deref()).await;
-    .await
+        let dest_id = ctx.resolve(identifier.as_deref()).await;
+        let fwd = forward::ForwardInfo::new(
+            peer,
+            local,
+            client.is_tls(),
+            Some(announced),
+            ctx.config.server.proxy_ttl,
+        );
+
+        let mut frame = format!("AUTH {} ", mechanism_name(&mech));
+        BASE64.encode_append(&raw_challenge, &mut frame);
+        frame.push_str("\r\n");
+        let auth = common::AuthFrame::inline(frame.into_bytes());
+
+        let resume = common::bridge_authenticated(
+            ctx,
+            &dest_id,
+            client,
+            peer,
+            identifier.as_deref(),
+            residual,
+            started,
+            "submission",
+            common::AuthWire::Smtp,
+            &auth,
+            b"421 4.3.0 backend unavailable\r\n",
+            MAX_PREAUTH,
+            || open_backend(ctx, &dest_id, &fwd),
+        )
+        .await?;
+
+        let Some(common::Resume {
+            stream: client,
+            buf,
+        }) = resume
+        else {
+            return Ok(());
+        };
+        if bump(&mut state.auth_failures, listener.max_auth_attempts) {
+            return Ok(());
+        }
+        stream = client;
+        state.buf = buf;
+    }
 }
 
 async fn preauth(
@@ -106,21 +145,17 @@ async fn preauth(
     listener: &ListenerConfig,
     caps: &SubmissionCapabilities,
     mut stream: BoxedStream,
-    local: SocketAddr,
+    hostname: &str,
+    state: &mut SubmissionState,
 ) -> Result<Option<SubmissionHandoff>> {
     let mut is_tls = stream.is_tls();
     let starttls_listener = listener.tls == TlsMode::Starttls;
-    let hostname = ctx.config.server.hostname_for(local);
 
-    write(
+    let SubmissionState {
-        &mut stream,
+        buf,
-        format!("220 {hostname} ESMTP {}\r\n", caps.banner).as_bytes(),
+        auth_failures,
-    )
+        ehlo_host,
-    .await?;
+    } = state;
-
-    let mut buf: Vec<u8> = Vec::with_capacity(1024);
-    let mut ehlo_host = String::new();
-    let mut auth_failures = 0u32;
 
     loop {
         let mut it = buf.iter();
@@ -133,10 +168,10 @@ async fn preauth(
                 let plain_ok = plain_auth_allowed(caps.allow_plain_auth_without_tls, is_tls);
                 match req {
                     Request::Ehlo { host } | Request::Lhlo { host } => {
-                        ehlo_host = host.to_string();
+                        *ehlo_host = host.to_string();
                         let resp = ehlo_response(
-                            &hostname,
+                            hostname,
-                            &ehlo_host,
+                            ehlo_host,
                             caps,
                             starttls_listener && !is_tls,
                             plain_ok,
@@ -145,7 +180,7 @@ async fn preauth(
                         buf.drain(..consumed);
                     }
                     Request::Helo { host } => {
-                        ehlo_host = host.to_string();
+                        *ehlo_host = host.to_string();
                         write(&mut stream, format!("250 {hostname}\r\n").as_bytes()).await?;
                         buf.drain(..consumed);
                     }
@@ -187,17 +222,17 @@ async fn preauth(
                             ctx,
                             plain_ok,
                             login_offered: common::sasl_offered(&caps.sasl, "LOGIN"),
-                            ehlo_host: &ehlo_host,
+                            ehlo_host,
                             max_attempts: listener.max_auth_attempts,
                         };
                         match handle_auth(
                             &params,
                             &mut stream,
-                            &mut buf,
+                            buf,
                             consumed,
                             mechanism,
                             &ir,
-                            &mut auth_failures,
+                            &mut *auth_failures,
                         )
                         .await?
                         {
@@ -233,7 +268,7 @@ async fn preauth(
                 if buf.len() > MAX_PREAUTH {
                     return Err(ProxyError::preauth("smtp line too long"));
                 }
-                let n = common::fill(&mut stream, &mut buf, MAX_PREAUTH + 8192).await?;
+                let n = common::fill(&mut stream, buf, MAX_PREAUTH + 8192).await?;
                 if n == 0 {
                     return Ok(None);
                 }
@@ -242,8 +277,7 @@ async fn preauth(
                 let drop_to = if consumed == 0 { buf.len() } else { consumed };
                 buf.drain(..drop_to);
                 write(&mut stream, b"500 5.5.2 Syntax error\r\n").await?;
-                auth_failures += 1;
+                if bump(auth_failures, listener.max_auth_attempts) {
-                if auth_failures >= listener.max_auth_attempts {
                     return Ok(None);
                 }
             }
@@ -332,7 +366,7 @@ async fn handle_auth(
         line
     };
 
-    let Some(raw) = decode_sasl_ir(&raw_b64) else {
+    let Ok(raw) = SASL_RESPONSE.decode(&raw_b64) else {
         return fail(
             stream,
             buf,
@@ -448,8 +482,7 @@ async fn cancelled(
     max_attempts: u32,
 ) -> Result<AuthStep> {
     write(&mut *stream, b"501 5.7.0 Authentication cancelled\r\n").await?;
-    *auth_failures += 1;
+    if bump(auth_failures, max_attempts) {
-    if *auth_failures >= max_attempts {
         Ok(AuthStep::Close)
     } else {
         Ok(AuthStep::Continue)
@@ -468,8 +501,7 @@ async fn fail(
         buf.drain(..drain);
     }
     write(&mut *stream, format!("535 {message}\r\n").as_bytes()).await?;
-    *auth_failures += 1;
+    if bump(auth_failures, max_attempts) {
-    if *auth_failures >= max_attempts {
         Ok(AuthStep::Close)
     } else {
         Ok(AuthStep::Continue)

src/route/mod.rs

@@ -164,17 +164,21 @@ impl Router {
     }
 
     pub async fn resolve(&self, identifier: Option<&str>) -> Arc<str> {
+        self.resolve_or(identifier, &self.default_destination).await
+    }
+
+    pub async fn resolve_or(&self, identifier: Option<&str>, default: &Arc<str>) -> Arc<str> {
         let key: Cow<'_, str> = match identifier {
             Some(id) => match self.normalize {
                 Normalize::None => Cow::Borrowed(id),
                 Normalize::Lowercase => Cow::Owned(id.to_lowercase()),
             },
-            None => return self.default_destination.clone(),
+            None => return default.clone(),
         };
 
         if let Some(hit) = self.cache.get(key.as_ref()).await {
             self.stats.hits.fetch_add(1, Ordering::Relaxed);
-            return hit.dest(&self.default_destination);
+            return hit.dest(default);
         }
         self.stats.misses.fetch_add(1, Ordering::Relaxed);
 
@@ -215,7 +219,7 @@ impl Router {
             .try_get_with(key.into_boxed_str(), init)
             .await
             .unwrap_or(Route::Transient);
-        route.dest(&self.default_destination)
+        route.dest(default)
     }
 
     pub fn normalize(&self, identifier: &str) -> String {

src/sasl.rs

@@ -4,6 +4,10 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
+use encodify::base64::{self, Base64};
+
+pub const SASL_RESPONSE: Base64 = base64::LENIENT;
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Credential {
     Plain {
@@ -98,10 +102,6 @@ pub fn extract_oauth_bearer(bytes: &[u8]) -> Option<(String, Option<String>)> {
     None
 }
 
-pub fn decode_sasl_ir(b64: &[u8]) -> Option<Vec<u8>> {
-    mail_parser::decoders::base64::base64_decode(b64)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -154,7 +154,7 @@ mod tests {
 
     #[test]
     fn lenient_ir_decode() {
-        let out = decode_sasl_ir(b"dGVzdAB0ZXN0AHRlc3Q=").unwrap();
+        let out = SASL_RESPONSE.decode(b"dGVzdAB0ZXN0AHRlc3Q=").unwrap();
         assert_eq!(out, b"test\0test\0test");
     }
 
@@ -204,13 +204,13 @@ mod tests {
 
     #[test]
     fn lenient_ir_tolerates_whitespace() {
-        let with_ws = decode_sasl_ir(b"dGVz dAB0\nZXN0AHRlc3Q=").unwrap();
+        let with_ws = SASL_RESPONSE.decode(b"dGVz dAB0\nZXN0AHRlc3Q=").unwrap();
         assert_eq!(with_ws, b"test\0test\0test");
     }
 
     #[test]
     fn lenient_ir_decodes_full_quads_without_padding() {
-        let out = decode_sasl_ir(b"AHRlc3QAc2VjcmV0").unwrap();
+        let out = SASL_RESPONSE.decode(b"AHRlc3QAc2VjcmV0").unwrap();
         assert_eq!(out, b"\0test\0secret");
     }
 }

src/tests/admin.rs

@@ -324,6 +324,14 @@ async fn admin_delay_holds_new_login() {
     )
     .await;
     assert_eq!(status, 400);
+    let (status, _) = admin_request(
+        admin_addr,
+        "POST",
+        "/connections/delay?identifier=user@example.com&seconds=18446744073709551615",
+        Some(TOKEN),
+    )
+    .await;
+    assert_eq!(status, 400);
 
     let listener = ctx.config.listener["pop3"].clone();
     let (mut client, server) = tcp_pair().await;
@@ -645,3 +653,164 @@ async fn admin_config_reload_rejects_invalid() {
         "legacy"
     );
 }
+
+fn switch_config(old_port: u16, new_port: u16, mapping_path: &str) -> String {
+    format!(
+        r#"
+[mapping]
+source = "file"
+normalize = "lowercase"
+[mapping.file]
+path = "{mapping_path}"
+
+[capabilities.pop3]
+allow_plain_auth_without_tls = true
+
+[routing]
+default_destination = "legacy"
+
+[destination.legacy]
+host = "127.0.0.1"
+forwarding = "none"
+allow_plaintext_auth = true
+[destination.legacy.protocol.pop3]
+port = {old_port}
+tls = "plain"
+
+[destination.next]
+host = "127.0.0.1"
+forwarding = "none"
+allow_plaintext_auth = true
+[destination.next.protocol.pop3]
+port = {new_port}
+tls = "plain"
+
+[listener.pop3]
+protocol = "pop3"
+bind = ["127.0.0.1:0"]
+tls = "plain"
+
+[admin]
+bind = "127.0.0.1:0"
+tls = "implicit"
+bearer_token = "{TOKEN}"
+min_token_len = 32
+lockout_threshold = 100
+lockout_duration = "5m"
+"#
+    )
+}
+
+async fn pop3_named_backend(name: &'static str) -> (u16, tokio::task::JoinHandle<()>) {
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+
+    dummy_backend(move |mut sock| async move {
+        sock.write_all(b"+OK ready\r\n").await.unwrap();
+        let mut buf = Vec::new();
+        let mut scratch = [0u8; 1024];
+        while find(&buf, b"AUTH PLAIN").is_none() || find(&buf, b"\r\n").is_none() {
+            let n = sock.read(&mut scratch).await.unwrap();
+            if n == 0 {
+                return;
+            }
+            buf.extend_from_slice(&scratch[..n]);
+        }
+        sock.write_all(format!("+OK logged in at {name}\r\n").as_bytes())
+            .await
+            .unwrap();
+        let _ = sock.read(&mut scratch).await;
+    })
+    .await
+}
+
+async fn held_login_follows_mapping_change(method: &str, path: &str, mapping_update: Option<&str>) {
+    use tokio::io::AsyncReadExt;
+
+    let (old_port, old_backend) = pop3_named_backend("legacy").await;
+    let (new_port, new_backend) = pop3_named_backend("next").await;
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = switch_config(old_port, new_port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+
+    let admin_listener = TcpListener::bind(unused_addr()).await.unwrap();
+    let admin_addr = admin_listener.local_addr().unwrap();
+    let admin_ctx = ctx.clone();
+    let admin_config = ctx.config.clone();
+    tokio::spawn(async move {
+        let shared = std::sync::Arc::new(arc_swap::ArcSwap::new(admin_ctx));
+        let _ = crate::admin::serve(shared, admin_config, None, admin_listener).await;
+    });
+
+    let (status, _) = admin_request(
+        admin_addr,
+        "POST",
+        "/connections/delay?identifier=user@example.com&seconds=60",
+        Some(TOKEN),
+    )
+    .await;
+    assert_eq!(status, 200);
+
+    let listener = ctx.config.listener["pop3"].clone();
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::pop3::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40000".parse().unwrap(),
+            "127.0.0.1:110".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let greeting = read_line(&mut client).await;
+    assert!(greeting.starts_with("+OK"), "greeting: {greeting}");
+    send(&mut client, b"USER user@example.com\r\nPASS secret\r\n").await;
+    tokio::time::sleep(std::time::Duration::from_millis(300)).await;
+
+    if let Some(contents) = mapping_update {
+        std::fs::write(mapping.path(), contents).unwrap();
+    }
+    let (status, _) = admin_request(admin_addr, method, path, Some(TOKEN)).await;
+    assert_eq!(status, 200);
+
+    let mut seen = Vec::new();
+    let mut scratch = [0u8; 1024];
+    while find(&seen, b"+OK logged in at").is_none() {
+        let n = tokio::time::timeout(std::time::Duration::from_secs(5), client.read(&mut scratch))
+            .await
+            .expect("held login was not released by the mapping change")
+            .unwrap();
+        assert!(n > 0, "client closed before login");
+        seen.extend_from_slice(&scratch[..n]);
+    }
+    assert!(
+        find(&seen, b"+OK logged in at next").is_some(),
+        "held login must reach the new destination, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+
+    drop(client);
+    let _ = new_backend.await;
+    old_backend.abort();
+    let _ = handler.await;
+}
+
+#[tokio::test]
+async fn admin_mapping_put_releases_held_login_to_new_destination() {
+    // a login held by /connections/delay goes to the destination set by PUT /mappings at once
+    held_login_follows_mapping_change(
+        "PUT",
+        "/mappings?identifier=user@example.com&destination=next",
+        None,
+    )
+    .await;
+}
+
+#[tokio::test]
+async fn admin_mappings_reload_releases_held_login_to_new_destination() {
+    // a login held by /connections/delay goes to the destination loaded by /mappings/reload at once
+    held_login_follows_mapping_change("POST", "/mappings/reload", Some("user@example.com\tnext\n"))
+        .await;
+}

src/tests/config_validation.rs

@@ -501,3 +501,79 @@ sasl = ["NTLM"]
         );
     }
 }
+
+fn http_fallback_config(mapping_path: &str, fallback: &str) -> String {
+    format!(
+        r#"
+{}
+[routing]
+default_destination = "legacy"
+
+[destination.legacy]
+host = "127.0.0.1"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.legacy.protocol.http]
+port = 80
+tls = "plain"
+
+[destination.imaponly]
+host = "127.0.0.1"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.imaponly.protocol.imap]
+port = 143
+tls = "plain"
+
+[[http.route]]
+match = "/**"
+extract = {{ from = "authorization" }}
+fallback = "{fallback}"
+"#,
+        mapping_block(mapping_path)
+    )
+}
+
+#[test]
+fn http_route_fallback_must_name_known_http_destination() {
+    let m = mapping_file("");
+    let path = m.path().display().to_string();
+    assert!(Config::parse_and_validate(&http_fallback_config(&path, "legacy")).is_ok());
+    assert!(Config::parse_and_validate(&http_fallback_config(&path, "ghost")).is_err());
+    assert!(Config::parse_and_validate(&http_fallback_config(&path, "imaponly")).is_err());
+}
+
+fn install_script_config() -> &'static str {
+    let script = include_str!("../../install.sh");
+    let (_, rest) = script
+        .split_once("write_config_file() {\n    cat > \"$1\" <<'EOF'\n")
+        .expect("install.sh config heredoc start");
+    let (config, _) = rest
+        .split_once("\nEOF\n")
+        .expect("install.sh config heredoc end");
+    config
+}
+
+#[test]
+fn shipped_configs_validate() {
+    // every configuration shipped with the proxy passes boot validation
+    for (name, raw) in [
+        (
+            "config.sample.toml",
+            include_str!("../../resources/config.sample.toml"),
+        ),
+        (
+            "config.stalwart-upgrade.toml",
+            include_str!("../../resources/config.stalwart-upgrade.toml"),
+        ),
+        (
+            "config.dovecot-postfix.toml",
+            include_str!("../../resources/config.dovecot-postfix.toml"),
+        ),
+        ("install.sh", install_script_config()),
+    ] {
+        if let Err(e) = Config::parse_and_validate(raw) {
+            panic!("{name} fails validation: {e}");
+        }
+    }
+}

src/tests/containers/clients.rs

@@ -4,8 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::Engine;
+use encodify::base64::STANDARD as B64;
-use base64::engine::general_purpose::STANDARD as B64;
 use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
 use tokio::net::TcpStream;
 

src/tests/containers/http.rs

@@ -6,6 +6,7 @@
 
 use std::sync::Arc;
 
+use encodify::base64::STANDARD as B64;
 use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
 use tokio::net::TcpStream;
 
@@ -34,11 +35,9 @@ impl Response {
 }
 
 pub fn basic_auth(user: &str, pass: &str) -> String {
-    use base64::Engine;
+    let mut header = String::from("Basic ");
-    format!(
+    B64.encode_append(format!("{user}:{pass}"), &mut header);
-        "Basic {}",
+    header
-        base64::engine::general_purpose::STANDARD.encode(format!("{user}:{pass}"))
-    )
 }
 
 pub async fn upgrade(

src/tests/containers/jmap.rs

@@ -55,7 +55,7 @@ tls = "implicit"
 [[http.route]]
 match = "/**"
 extract = {{ from = "authorization" }}
-fallback = "default"
+fallback = "new"
 
 [listener.http]
 protocol = "http"

src/tests/containers/master_user_and_load.rs

@@ -4,8 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::Engine;
+use encodify::base64::STANDARD as B64;
-use base64::engine::general_purpose::STANDARD as B64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::TcpStream;
 

src/tests/containers/oauth.rs

@@ -4,8 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::Engine;
+use encodify::base64::STANDARD as B64;
-use base64::engine::general_purpose::STANDARD as B64;
 use tokio::io::{AsyncRead, AsyncReadExt, AsyncWriteExt};
 use tokio::net::TcpStream;
 

src/tests/containers/scenario2.rs

@@ -163,7 +163,7 @@ tls = "implicit"
 [[http.route]]
 match = "/**"
 extract = {{ from = "authorization" }}
-fallback = "default"
+fallback = "old"
 
 [listener.http]
 protocol = "http"

src/tests/containers/stalwart.rs

@@ -830,7 +830,7 @@ fn path_of(url: &str) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use base64::Engine;
+    use encodify::base64::STANDARD as B64;
     use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
     async fn imaps_auth(host: &str, port: u16, login: &str, password: &str) -> String {
@@ -838,7 +838,7 @@ mod tests {
         let mut stream = crate::tests::harness::tls_connect_client(tcp).await;
         let mut buf = [0u8; 512];
         let _ = stream.read(&mut buf).await.unwrap();
-        let ir = base64::engine::general_purpose::STANDARD.encode(format!("\0{login}\0{password}"));
+        let ir = B64.encode(format!("\0{login}\0{password}"));
         stream
             .write_all(format!("a1 AUTHENTICATE PLAIN {ir}\r\n").as_bytes())
             .await

src/tests/containers/toolbox_http.rs

@@ -40,7 +40,7 @@ tls = "implicit"
 [[http.route]]
 match = "/**"
 extract = {{ from = "authorization" }}
-fallback = "default"
+fallback = "new"
 
 [listener.http]
 protocol = "http"

src/tests/forwarding.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::TcpStream;
 

src/tests/http_proxy.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 
 use super::harness::*;
 
@@ -516,6 +516,113 @@ tls = "plain"
     handler.abort();
 }
 
+#[tokio::test]
+async fn http_route_fallback_destination_used_without_mapping() {
+    async fn backend_default(mut sock: tokio::net::TcpStream) {
+        read_req_head(&mut sock).await;
+        sock.write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 7\r\nConnection: close\r\n\r\ndefault")
+            .await
+            .unwrap();
+    }
+    async fn backend_fallback(mut sock: tokio::net::TcpStream) {
+        read_req_head(&mut sock).await;
+        sock.write_all(
+            b"HTTP/1.1 200 OK\r\nContent-Length: 8\r\nConnection: close\r\n\r\nfallback",
+        )
+        .await
+        .unwrap();
+    }
+
+    let mapping = mapping_file("alice@x\tweb_default\n");
+    let mut handles = Vec::new();
+    let cases = [
+        (None, "fallback"),
+        (Some("nobody@x"), "fallback"),
+        (Some("alice@x"), "default"),
+    ];
+    for (user, expected) in cases {
+        let (port_d, bd) = dummy_backend(backend_default).await;
+        let (port_f, bf) = dummy_backend(backend_fallback).await;
+        handles.push(bd);
+        handles.push(bf);
+        let toml = format!(
+            r#"
+[mapping]
+source = "file"
+normalize = "lowercase"
+[mapping.file]
+path = "{}"
+
+[routing]
+default_destination = "web_default"
+
+[destination.web_default]
+host = "127.0.0.1"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.web_default.protocol.http]
+port = {port_d}
+tls = "plain"
+
+[destination.web_fallback]
+host = "127.0.0.1"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.web_fallback.protocol.http]
+port = {port_f}
+tls = "plain"
+
+[[http.route]]
+match = "/**"
+extract = {{ from = "authorization" }}
+fallback = "web_fallback"
+
+[listener.http]
+protocol = "http"
+bind = ["127.0.0.1:0"]
+tls = "plain"
+"#,
+            mapping.path().display()
+        );
+        let ctx = make_ctx(&toml).await;
+        let listener = ctx.config.listener["http"].clone();
+        let (mut client, srv) = tcp_pair().await;
+        let handler = tokio::spawn(async move {
+            let _ = crate::http::proxy::handle(
+                &ctx,
+                &listener,
+                Box::new(srv),
+                "127.0.0.1:40044".parse().unwrap(),
+                "127.0.0.1:80".parse().unwrap(),
+            )
+            .await;
+        });
+        let auth = user
+            .map(|u| {
+                format!(
+                    "Authorization: Basic {}\r\n",
+                    BASE64.encode(format!("{u}:pw"))
+                )
+            })
+            .unwrap_or_default();
+        send(
+            &mut client,
+            format!("GET / HTTP/1.1\r\nHost: x\r\n{auth}Connection: close\r\n\r\n").as_bytes(),
+        )
+        .await;
+        let resp = read_to_eof(&mut client).await;
+        assert!(
+            resp.ends_with(expected.as_bytes()),
+            "user {user:?} should reach {expected}, got {:?}",
+            String::from_utf8_lossy(&resp)
+        );
+        handles.push(handler);
+    }
+    for h in handles {
+        h.abort();
+    }
+}
+
 async fn read_until_backend(sock: &mut tokio::net::TcpStream, needle: &[u8]) -> Vec<u8> {
     let mut buf = Vec::new();
     let mut scratch = [0u8; 1024];
@@ -985,3 +1092,443 @@ async fn http_chunked_request_and_response_round_trip() {
     let _ = backend.await;
     handler.abort();
 }
+
+fn extract_http_config(host: &str, port: u16, mapping_path: &str) -> String {
+    format!(
+        r#"
+[mapping]
+source = "file"
+normalize = "lowercase"
+[mapping.file]
+path = "{mapping_path}"
+
+[routing]
+default_destination = "web"
+
+[destination.web]
+host = "{host}"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.web.protocol.http]
+port = {port}
+tls = "plain"
+
+[[http.route]]
+match = "/**"
+extract = {{ from = "authorization" }}
+
+[listener.http]
+protocol = "http"
+bind = ["127.0.0.1:0"]
+tls = "plain"
+"#
+    )
+}
+
+#[tokio::test]
+async fn http_authenticated_keepalive_connection_is_kickable() {
+    async fn backend(mut sock: tokio::net::TcpStream) {
+        read_req_head(&mut sock).await;
+        sock.write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 2\r\n\r\nok")
+            .await
+            .unwrap();
+        let mut sink = [0u8; 1024];
+        loop {
+            match sock.read(&mut sink).await {
+                Ok(0) | Err(_) => break,
+                Ok(_) => {}
+            }
+        }
+    }
+
+    let (port, backend) = dummy_backend(backend).await;
+    let mapping = mapping_file("user@example.com\tweb\n");
+    let toml = extract_http_config("127.0.0.1", port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40070".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let creds = BASE64.encode("user@example.com:pw");
+    let req = format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {creds}\r\n\r\n");
+    send(&mut client, req.as_bytes()).await;
+    let resp = read_until(&mut client, b"ok").await;
+    assert!(find(&resp, b"200").is_some(), "expected 200");
+
+    assert_eq!(
+        ctx.conns.kick(&ctx.router.normalize("user@example.com")),
+        1,
+        "an authenticated http connection must be registered for its account"
+    );
+
+    let n = tokio::time::timeout(
+        std::time::Duration::from_secs(5),
+        client.read(&mut [0u8; 64]),
+    )
+    .await
+    .expect("kick did not disconnect the client in time")
+    .unwrap();
+    assert_eq!(n, 0, "expected EOF after kick, got {n} bytes");
+
+    let _ = backend.await;
+    handler.abort();
+}
+
+#[tokio::test]
+async fn http_websocket_bridge_is_kickable() {
+    async fn backend(mut sock: tokio::net::TcpStream) {
+        read_req_head(&mut sock).await;
+        sock.write_all(
+            b"HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=\r\n\r\n",
+        )
+        .await
+        .unwrap();
+        let mut sink = [0u8; 1024];
+        loop {
+            match sock.read(&mut sink).await {
+                Ok(0) | Err(_) => break,
+                Ok(_) => {}
+            }
+        }
+    }
+
+    let (port, backend) = dummy_backend(backend).await;
+    let mapping = mapping_file("user@example.com\tweb\n");
+    let toml = extract_http_config("127.0.0.1", port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40071".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let creds = BASE64.encode("user@example.com:pw");
+    let req = format!(
+        "GET /ws HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {creds}\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n\r\n"
+    );
+    send(&mut client, req.as_bytes()).await;
+
+    let upgrade = read_until(&mut client, b"\r\n\r\n").await;
+    assert!(find(&upgrade, b"101").is_some(), "expected the 101 upgrade");
+
+    assert_eq!(
+        ctx.conns.kick(&ctx.router.normalize("user@example.com")),
+        1,
+        "an upgraded websocket must stay registered for its account"
+    );
+
+    let n = tokio::time::timeout(
+        std::time::Duration::from_secs(5),
+        client.read(&mut [0u8; 64]),
+    )
+    .await
+    .expect("kick did not disconnect the websocket in time")
+    .unwrap();
+    assert_eq!(n, 0, "expected EOF after kick, got {n} bytes");
+
+    let _ = backend.await;
+    handler.abort();
+}
+
+#[tokio::test]
+async fn http_keepalive_rejects_a_second_account_with_421() {
+    async fn backend(mut sock: tokio::net::TcpStream) {
+        for _ in 0..2 {
+            read_req_head(&mut sock).await;
+            if sock
+                .write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 2\r\n\r\nok")
+                .await
+                .is_err()
+            {
+                return;
+            }
+        }
+        let mut sink = [0u8; 1024];
+        loop {
+            match sock.read(&mut sink).await {
+                Ok(0) | Err(_) => break,
+                Ok(_) => {}
+            }
+        }
+    }
+
+    let (port, backend) = dummy_backend(backend).await;
+    let mapping = mapping_file("user@example.com\tweb\nother@example.com\tweb\n");
+    let toml = extract_http_config("127.0.0.1", port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40072".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let first = BASE64.encode("user@example.com:pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {first}\r\n\r\n").as_bytes(),
+    )
+    .await;
+    let resp = read_until(&mut client, b"ok").await;
+    assert!(
+        find(&resp, b"200").is_some(),
+        "expected 200 for the pinned account"
+    );
+
+    let second = BASE64.encode("other@example.com:pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {second}\r\n\r\n")
+            .as_bytes(),
+    )
+    .await;
+    let tail = read_to_eof(&mut client).await;
+    assert!(
+        find(&tail, b"421").is_some(),
+        "a second account on a pinned connection must get 421, got {:?}",
+        String::from_utf8_lossy(&tail)
+    );
+
+    let _ = backend.await;
+    handler.abort();
+}
+
+#[tokio::test]
+async fn http_empty_identifier_does_not_pin_or_register_the_connection() {
+    async fn backend(mut sock: tokio::net::TcpStream) {
+        for _ in 0..2 {
+            read_req_head(&mut sock).await;
+            if sock
+                .write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 2\r\n\r\nok")
+                .await
+                .is_err()
+            {
+                return;
+            }
+        }
+        let mut sink = [0u8; 1024];
+        loop {
+            match sock.read(&mut sink).await {
+                Ok(0) | Err(_) => break,
+                Ok(_) => {}
+            }
+        }
+    }
+
+    let (port, backend) = dummy_backend(backend).await;
+    let mapping = mapping_file("user@example.com\tweb\n");
+    let toml = extract_http_config("127.0.0.1", port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40073".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let empty = BASE64.encode(":pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {empty}\r\n\r\n").as_bytes(),
+    )
+    .await;
+    let first = read_until(&mut client, b"ok").await;
+    assert!(
+        find(&first, b"200").is_some(),
+        "expected 200 for the empty login"
+    );
+
+    assert_eq!(
+        ctx.conns.kick(""),
+        0,
+        "an empty identifier must not be registered as an account"
+    );
+
+    let creds = BASE64.encode("user@example.com:pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {creds}\r\n\r\n").as_bytes(),
+    )
+    .await;
+    let second = read_until(&mut client, b"ok").await;
+    assert!(
+        find(&second, b"421").is_none(),
+        "an empty first login must not pin the connection, got {:?}",
+        String::from_utf8_lossy(&second)
+    );
+    assert_eq!(
+        ctx.conns.kick(&ctx.router.normalize("user@example.com")),
+        1,
+        "the real account must be the one registered"
+    );
+
+    let _ = backend.await;
+    handler.abort();
+}
+
+#[tokio::test]
+async fn http_login_delay_holds_an_authenticated_request() {
+    async fn backend(mut sock: tokio::net::TcpStream) {
+        read_req_head(&mut sock).await;
+        let _ = sock
+            .write_all(b"HTTP/1.1 200 OK\r\nContent-Length: 2\r\nConnection: close\r\n\r\nok")
+            .await;
+    }
+
+    let (port, backend) = dummy_backend(backend).await;
+    let mapping = mapping_file("user@example.com\tweb\n");
+    let toml = extract_http_config("127.0.0.1", port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+
+    ctx.conns.set_delay(
+        &ctx.router.normalize("user@example.com"),
+        std::time::Instant::now() + std::time::Duration::from_millis(1500),
+    );
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40075".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let started = std::time::Instant::now();
+    let creds = BASE64.encode("user@example.com:pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {creds}\r\nConnection: close\r\n\r\n").as_bytes(),
+    )
+    .await;
+    let resp = read_to_eof(&mut client).await;
+    assert!(find(&resp, b"200").is_some(), "expected 200");
+    assert!(
+        started.elapsed() >= std::time::Duration::from_millis(1400),
+        "the login delay must hold an http request too, elapsed {:?}",
+        started.elapsed()
+    );
+
+    let _ = backend.await;
+    handler.abort();
+}
+
+#[tokio::test]
+async fn http_held_login_follows_mapping_change() {
+    // an http request held by a login delay is sent to the destination mapped when the hold ends
+    async fn backend(name: &'static str) -> (u16, tokio::task::JoinHandle<()>) {
+        dummy_backend(move |mut sock| async move {
+            read_req_head(&mut sock).await;
+            let _ = sock
+                .write_all(
+                    format!(
+                        "HTTP/1.1 200 OK\r\nContent-Length: {}\r\nConnection: close\r\n\r\n{name}",
+                        name.len()
+                    )
+                    .as_bytes(),
+                )
+                .await;
+        })
+        .await
+    }
+
+    let (old_port, old_backend) = backend("legacy").await;
+    let (new_port, new_backend) = backend("next").await;
+    let mapping = mapping_file("user@example.com\tweb\n");
+    let toml = format!(
+        r#"{}
+[destination.next]
+host = "127.0.0.1"
+proxy_protocol = false
+allow_plaintext_auth = true
+[destination.next.protocol.http]
+port = {new_port}
+tls = "plain"
+"#,
+        extract_http_config("127.0.0.1", old_port, &mapping.path().display().to_string())
+    );
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["http"].clone();
+    let identifier = ctx.router.normalize("user@example.com");
+    ctx.conns.set_delay(
+        &identifier,
+        std::time::Instant::now() + std::time::Duration::from_secs(60),
+    );
+
+    let (mut client, srv) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::http::proxy::handle(
+            &ctx2,
+            &listener,
+            Box::new(srv),
+            "127.0.0.1:40076".parse().unwrap(),
+            "127.0.0.1:80".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let creds = BASE64.encode("user@example.com:pw");
+    send(
+        &mut client,
+        format!("GET /jmap HTTP/1.1\r\nHost: x\r\nAuthorization: Basic {creds}\r\nConnection: close\r\n\r\n").as_bytes(),
+    )
+    .await;
+    tokio::time::sleep(std::time::Duration::from_millis(300)).await;
+    ctx.router.upsert("user@example.com", "next").await.unwrap();
+    ctx.conns.release_delay(&identifier);
+
+    let resp = tokio::time::timeout(std::time::Duration::from_secs(5), read_to_eof(&mut client))
+        .await
+        .expect("held request was not released by the mapping change");
+    assert!(
+        find(&resp, b"\r\n\r\nnext").is_some(),
+        "held request must reach the new destination, got {:?}",
+        String::from_utf8_lossy(&resp)
+    );
+
+    let _ = new_backend.await;
+    old_backend.abort();
+    handler.abort();
+}

src/tests/imap.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
 use super::harness::*;
@@ -801,3 +801,175 @@ async fn imap_keeps_inline_initial_response_when_backend_advertises_sasl_ir() {
     let _ = backend.await;
     handler.abort();
 }
+
+#[tokio::test]
+async fn imap_pipelined_command_after_failed_auth_is_parsed_not_bridged() {
+    let (port, backend) = dummy_backend(|mut sock| async move {
+        sock.write_all(b"* OK [CAPABILITY IMAP4rev2 SASL-IR] backend ready\r\n")
+            .await
+            .unwrap();
+        let mut buf = Vec::new();
+        let mut scratch = [0u8; 1024];
+        while find(&buf, b"AUTHENTICATE").is_none() || find(&buf, b"\r\n").is_none() {
+            match sock.read(&mut scratch).await {
+                Ok(0) | Err(_) => return,
+                Ok(n) => buf.extend_from_slice(&scratch[..n]),
+            }
+        }
+        let _ = sock
+            .write_all(b"a1 NO [AUTHENTICATIONFAILED] nope\r\n")
+            .await;
+        let mut sink = [0u8; 1024];
+        loop {
+            match sock.read(&mut sink).await {
+                Ok(0) | Err(_) => break,
+                Ok(n) => {
+                    assert!(
+                        find(&sink[..n], b"CAPABILITY").is_none(),
+                        "pipelined client bytes must not reach the backend after a failed auth"
+                    );
+                }
+            }
+        }
+    })
+    .await;
+
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = config(port, &mapping.path().display().to_string());
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["imap"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::imap::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40010".parse().unwrap(),
+            "127.0.0.1:143".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(
+        &mut client,
+        b"a1 LOGIN user@example.com wrong\r\na2 CAPABILITY\r\n",
+    )
+    .await;
+
+    let seen = read_until(&mut client, b"a2 OK").await;
+    assert!(
+        find(&seen, b"a1 NO").is_some(),
+        "expected the backend rejection, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+    assert!(
+        find(&seen, b"a2 OK CAPABILITY completed").is_some(),
+        "the pipelined command must be answered by the proxy, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+
+    drop(client);
+    let _ = backend.await;
+    let _ = handler.await;
+}
+
+async fn preauth_only_ctx() -> (
+    std::sync::Arc<crate::proto::common::Ctx>,
+    tokio::task::JoinHandle<()>,
+) {
+    let (port, backend) = dummy_backend(|_sock| async move {}).await;
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = config(port, &mapping.path().display().to_string());
+    (make_ctx(&toml).await, backend)
+}
+
+#[tokio::test]
+async fn imap_rejected_sasl_response_is_not_reparsed_as_a_command() {
+    let (ctx, backend) = preauth_only_ctx().await;
+    let listener = ctx.config.listener["imap"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::imap::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40011".parse().unwrap(),
+            "127.0.0.1:143".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(
+        &mut client,
+        b"a1 AUTHENTICATE PLAIN\r\n@@@\r\na2 CAPABILITY\r\n",
+    )
+    .await;
+
+    let seen = read_until(&mut client, b"a2 OK").await;
+    assert!(
+        find(&seen, b"a1 NO").is_some(),
+        "expected the SASL response to be rejected, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+    assert!(
+        find(&seen, b"* BAD").is_none(),
+        "the rejected SASL response must not be re-parsed as a command, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+    assert!(
+        find(&seen, b"a2 OK CAPABILITY completed").is_some(),
+        "the pipelined command must still be answered, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+
+    drop(client);
+    backend.abort();
+    let _ = handler.await;
+}
+
+#[tokio::test]
+async fn imap_command_pipelined_behind_a_rejected_sasl_response_is_not_lost() {
+    let (ctx, backend) = preauth_only_ctx().await;
+    let listener = ctx.config.listener["imap"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::imap::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40012".parse().unwrap(),
+            "127.0.0.1:143".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(&mut client, b"a1 AUTHENTICATE PLAIN\r\n").await;
+    let challenge = read_until(&mut client, b"+ ").await;
+    assert!(find(&challenge, b"+ ").is_some(), "expected a continuation");
+
+    send(&mut client, b"@@@\r\na2 CAPABILITY\r\n").await;
+    let seen = read_until(&mut client, b"a2 OK").await;
+    assert!(
+        find(&seen, b"a1 NO").is_some(),
+        "expected the SASL response to be rejected, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+    assert!(
+        find(&seen, b"a2 OK CAPABILITY completed").is_some(),
+        "the command behind the rejected response must not be dropped, got {:?}",
+        String::from_utf8_lossy(&seen)
+    );
+
+    drop(client);
+    backend.abort();
+    let _ = handler.await;
+}

src/tests/managesieve.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
 use super::harness::*;

src/tests/pop3.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
 use super::harness::*;
@@ -609,3 +609,366 @@ tls = "plain"
         String::from_utf8_lossy(&resp)
     );
 }
+
+fn retry_config(backend_port: u16, mapping_path: &str, max_auth_attempts: u32) -> String {
+    format!(
+        r#"
+[mapping]
+source = "file"
+normalize = "lowercase"
+[mapping.file]
+path = "{mapping_path}"
+
+[capabilities.pop3]
+allow_plain_auth_without_tls = true
+
+[routing]
+default_destination = "legacy"
+
+[destination.legacy]
+host = "127.0.0.1"
+forwarding = "none"
+allow_plaintext_auth = true
+[destination.legacy.protocol.pop3]
+port = {backend_port}
+tls = "plain"
+
+[listener.pop3]
+protocol = "pop3"
+bind = ["127.0.0.1:0"]
+tls = "plain"
+max_auth_attempts = {max_auth_attempts}
+"#
+    )
+}
+
+async fn rejecting_backend(
+    attempts: std::sync::Arc<std::sync::atomic::AtomicUsize>,
+) -> (u16, tokio::task::JoinHandle<()>) {
+    let listener = tokio::net::TcpListener::bind(unused_addr()).await.unwrap();
+    let port = listener.local_addr().unwrap().port();
+    let handle = tokio::spawn(async move {
+        while let Ok((mut sock, _)) = listener.accept().await {
+            attempts.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
+            let _ = sock.set_nodelay(true);
+            tokio::spawn(async move {
+                if sock.write_all(b"+OK ready\r\n").await.is_err() {
+                    return;
+                }
+                let mut buf = Vec::new();
+                let mut scratch = [0u8; 1024];
+                while find(&buf, b"\r\n").is_none() {
+                    match sock.read(&mut scratch).await {
+                        Ok(0) | Err(_) => return,
+                        Ok(n) => buf.extend_from_slice(&scratch[..n]),
+                    }
+                }
+                let _ = sock.write_all(b"-ERR bad password\r\n").await;
+                let mut sink = [0u8; 1024];
+                loop {
+                    match sock.read(&mut sink).await {
+                        Ok(0) | Err(_) => break,
+                        Ok(_) => {}
+                    }
+                }
+            });
+        }
+    });
+    (port, handle)
+}
+
+#[tokio::test]
+async fn pop3_failed_backend_auth_does_not_hand_the_client_a_raw_bridge() {
+    let attempts = std::sync::Arc::new(std::sync::atomic::AtomicUsize::new(0));
+    let (backend_port, backend) = rejecting_backend(attempts.clone()).await;
+
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = retry_config(backend_port, &mapping.path().display().to_string(), 10);
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["pop3"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::pop3::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40000".parse().unwrap(),
+            "127.0.0.1:110".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let greeting = read_line(&mut client).await;
+    assert!(greeting.starts_with("+OK"), "greeting: {greeting}");
+
+    send(&mut client, b"USER user@example.com\r\nPASS wrong\r\n").await;
+    let failure = read_until(&mut client, b"-ERR").await;
+    assert!(find(&failure, b"-ERR").is_some(), "expected a rejection");
+
+    send(&mut client, b"CAPA\r\n").await;
+    let capa = read_until(&mut client, b"\r\n.\r\n").await;
+    assert!(
+        find(&capa, b"USER").is_some(),
+        "the proxy must still be parsing after a failed auth, got {:?}",
+        String::from_utf8_lossy(&capa)
+    );
+    assert_eq!(
+        attempts.load(std::sync::atomic::Ordering::SeqCst),
+        1,
+        "CAPA must be answered by the proxy, not forwarded to a backend"
+    );
+
+    drop(client);
+    backend.abort();
+    let _ = handler.await;
+}
+
+#[tokio::test]
+async fn pop3_rejected_auth_closes_the_backend_leg_with_quit() {
+    let (backend_port, backend) = dummy_backend(|mut sock| async move {
+        sock.write_all(b"+OK ready\r\n").await.unwrap();
+        let mut buf = Vec::new();
+        let mut scratch = [0u8; 1024];
+        while find(&buf, b"\r\n").is_none() {
+            match sock.read(&mut scratch).await {
+                Ok(0) | Err(_) => return,
+                Ok(n) => buf.extend_from_slice(&scratch[..n]),
+            }
+        }
+        let _ = sock.write_all(b"-ERR bad password\r\n").await;
+        buf.clear();
+        loop {
+            match sock.read(&mut scratch).await {
+                Ok(0) | Err(_) => break,
+                Ok(n) => buf.extend_from_slice(&scratch[..n]),
+            }
+        }
+        assert!(
+            find(&buf, b"QUIT").is_some(),
+            "backend leg must be closed with QUIT, saw {:?}",
+            String::from_utf8_lossy(&buf)
+        );
+    })
+    .await;
+
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = retry_config(backend_port, &mapping.path().display().to_string(), 10);
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["pop3"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::pop3::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40003".parse().unwrap(),
+            "127.0.0.1:110".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(&mut client, b"USER user@example.com\r\nPASS wrong\r\n").await;
+    let _ = read_until(&mut client, b"-ERR").await;
+
+    drop(client);
+    backend.await.expect("backend assertion failed");
+    let _ = handler.await;
+}
+
+#[tokio::test]
+async fn pop3_backend_auth_failures_count_toward_max_auth_attempts() {
+    let attempts = std::sync::Arc::new(std::sync::atomic::AtomicUsize::new(0));
+    let (backend_port, backend) = rejecting_backend(attempts.clone()).await;
+
+    let mapping = mapping_file("user@example.com\tlegacy\n");
+    let toml = retry_config(backend_port, &mapping.path().display().to_string(), 2);
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["pop3"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::pop3::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40001".parse().unwrap(),
+            "127.0.0.1:110".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(&mut client, b"USER user@example.com\r\nPASS wrong\r\n").await;
+    let _ = read_until(&mut client, b"-ERR").await;
+    send(&mut client, b"USER user@example.com\r\nPASS wrong\r\n").await;
+
+    let tail = read_to_eof(&mut client).await;
+    assert!(
+        find(&tail, b"-ERR").is_some(),
+        "expected the second rejection, got {:?}",
+        String::from_utf8_lossy(&tail)
+    );
+    assert_eq!(
+        attempts.load(std::sync::atomic::Ordering::SeqCst),
+        2,
+        "max_auth_attempts must bound the backend connections a client can force"
+    );
+
+    backend.abort();
+    let _ = handler.await;
+}
+
+#[tokio::test]
+async fn pop3_retry_after_failed_auth_is_routed_and_registered_for_its_own_account() {
+    async fn accepting_backend(
+        seen: std::sync::Arc<tokio::sync::Mutex<Vec<u8>>>,
+    ) -> (u16, tokio::task::JoinHandle<()>) {
+        let listener = tokio::net::TcpListener::bind(unused_addr()).await.unwrap();
+        let port = listener.local_addr().unwrap().port();
+        let handle = tokio::spawn(async move {
+            while let Ok((mut sock, _)) = listener.accept().await {
+                let seen = seen.clone();
+                let _ = sock.set_nodelay(true);
+                tokio::spawn(async move {
+                    if sock.write_all(b"+OK ready\r\n").await.is_err() {
+                        return;
+                    }
+                    let mut buf = Vec::new();
+                    let mut scratch = [0u8; 1024];
+                    while find(&buf, b"\r\n").is_none() {
+                        match sock.read(&mut scratch).await {
+                            Ok(0) | Err(_) => return,
+                            Ok(n) => buf.extend_from_slice(&scratch[..n]),
+                        }
+                    }
+                    seen.lock().await.extend_from_slice(&buf);
+                    let _ = sock.write_all(b"+OK logged in\r\n").await;
+                    let mut sink = [0u8; 1024];
+                    loop {
+                        match sock.read(&mut sink).await {
+                            Ok(0) | Err(_) => break,
+                            Ok(_) => {}
+                        }
+                    }
+                });
+            }
+        });
+        (port, handle)
+    }
+
+    let rejects = std::sync::Arc::new(std::sync::atomic::AtomicUsize::new(0));
+    let (legacy_port, legacy) = rejecting_backend(rejects.clone()).await;
+    let seen = std::sync::Arc::new(tokio::sync::Mutex::new(Vec::new()));
+    let (modern_port, modern) = accepting_backend(seen.clone()).await;
+
+    let mapping = mapping_file("alice@example.com\tlegacy\nbob@example.com\tmodern\n");
+    let toml = format!(
+        r#"
+[mapping]
+source = "file"
+normalize = "lowercase"
+[mapping.file]
+path = "{}"
+
+[capabilities.pop3]
+allow_plain_auth_without_tls = true
+
+[routing]
+default_destination = "legacy"
+
+[destination.legacy]
+host = "127.0.0.1"
+forwarding = "none"
+allow_plaintext_auth = true
+[destination.legacy.protocol.pop3]
+port = {legacy_port}
+tls = "plain"
+
+[destination.modern]
+host = "127.0.0.1"
+forwarding = "none"
+allow_plaintext_auth = true
+[destination.modern.protocol.pop3]
+port = {modern_port}
+tls = "plain"
+
+[listener.pop3]
+protocol = "pop3"
+bind = ["127.0.0.1:0"]
+tls = "plain"
+max_auth_attempts = 10
+"#,
+        mapping.path().display()
+    );
+
+    let ctx = make_ctx(&toml).await;
+    let listener = ctx.config.listener["pop3"].clone();
+
+    let (mut client, server) = tcp_pair().await;
+    let ctx2 = ctx.clone();
+    let handler = tokio::spawn(async move {
+        let _ = crate::proto::pop3::handle(
+            &ctx2,
+            &listener,
+            Box::new(server),
+            "203.0.113.9:40002".parse().unwrap(),
+            "127.0.0.1:110".parse().unwrap(),
+        )
+        .await;
+    });
+
+    let _ = read_line(&mut client).await;
+    send(&mut client, b"USER alice@example.com\r\nPASS wrong\r\n").await;
+    let _ = read_until(&mut client, b"-ERR").await;
+
+    send(&mut client, b"USER bob@example.com\r\nPASS right\r\n").await;
+    let ok = read_until(&mut client, b"+OK logged in").await;
+    assert!(
+        find(&ok, b"+OK logged in").is_some(),
+        "second account should authenticate, got {:?}",
+        String::from_utf8_lossy(&ok)
+    );
+
+    let replayed = seen.lock().await.clone();
+    let expected = BASE64.encode("\0bob@example.com\0right");
+    assert!(
+        find(&replayed, expected.as_bytes()).is_some(),
+        "the retry must be re-routed to bob's destination, backend saw {:?}",
+        String::from_utf8_lossy(&replayed)
+    );
+    assert_eq!(
+        rejects.load(std::sync::atomic::Ordering::SeqCst),
+        1,
+        "alice's destination must see only the first attempt"
+    );
+
+    assert_eq!(
+        ctx.conns.kick(&ctx.router.normalize("alice@example.com")),
+        0,
+        "the failed account must not hold a registration"
+    );
+    assert_eq!(
+        ctx.conns.kick(&ctx.router.normalize("bob@example.com")),
+        1,
+        "the account that actually authenticated must be kickable"
+    );
+
+    let n = tokio::time::timeout(
+        std::time::Duration::from_secs(5),
+        client.read(&mut [0u8; 64]),
+    )
+    .await
+    .expect("kick did not disconnect the client in time")
+    .unwrap();
+    assert_eq!(n, 0, "expected EOF after kick, got {n} bytes");
+
+    legacy.abort();
+    modern.abort();
+    let _ = handler.await;
+}

src/tests/routing.rs

@@ -63,6 +63,29 @@ async fn router_resolves_normalizes_and_caches() {
     assert_eq!(&*router.resolve(Some("user@example.com")).await, "primary");
 }
 
+#[tokio::test]
+async fn router_resolve_or_uses_given_fallback() {
+    let mapping = mapping_file("user@example.com\tprimary\n");
+    let toml = config(&mapping.path().display().to_string());
+    let router = build_router(&toml).await;
+    let fallback: std::sync::Arc<str> = "primary".into();
+    let legacy: std::sync::Arc<str> = "legacy".into();
+
+    assert_eq!(&*router.resolve_or(None, &fallback).await, "primary");
+    assert_eq!(
+        &*router.resolve_or(Some("nobody@x"), &fallback).await,
+        "primary"
+    );
+    assert_eq!(
+        &*router.resolve_or(Some("nobody@x"), &legacy).await,
+        "legacy"
+    );
+    assert_eq!(
+        &*router.resolve_or(Some("user@example.com"), &legacy).await,
+        "primary"
+    );
+}
+
 #[tokio::test]
 async fn router_cache_hits_and_misses() {
     let mapping = mapping_file("user@example.com\tprimary\n");

src/tests/smtp.rs

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::STANDARD as BASE64};
+use encodify::base64::STANDARD as BASE64;
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
 use super::harness::*;

src/token.rs

@@ -4,17 +4,14 @@
  * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-SEL
  */
 
-use base64::{Engine, engine::general_purpose::URL_SAFE_NO_PAD};
+use encodify::base64::URL_SAFE_NO_PAD;
 
 use crate::sasl::Credential;
 
 pub fn bearer_identifier(token: &str, jwt_username_claim: &str) -> Option<String> {
     if let Some(rest) = token.strip_prefix("sw1.") {
         return match rest.split_once('.') {
-            Some((_body, footer)) => {
+            Some((_body, footer)) => URL_SAFE_NO_PAD.decode_to_string(footer).ok(),
-                let decoded = URL_SAFE_NO_PAD.decode(footer).ok()?;
-                String::from_utf8(decoded).ok()
-            }
             None => None,
         };
     }
@@ -61,7 +58,6 @@ pub fn identifier_from_credential(cred: &Credential, jwt_username_claim: &str) -
 #[cfg(test)]
 mod tests {
     use super::*;
-    use base64::{Engine, engine::general_purpose::URL_SAFE_NO_PAD};
 
     #[test]
     fn sw1_footer() {