kumomta

Concepts

Queuing

Messages are assigned to a queue upon reception. The system can support arbitrarily named queues but the convention is to construct the queue name from some metadata associated with the message:

• tenant - some kind of sender or customer identifier or identity derived either from the message itself or authentication of the injection session.
• campaign - a sender-provided label that can be used to logically group a set of related messages, perhaps generated from the same campaign.
• destination domain - the site where the email will be routed

These three pieces of information are combined to produce the name of the queue in the form campaign:tenant@domain.

Debugging/Tracing

This will launch the server using the policy defined in simple_policy.lua:

KUMOD_LOG=kumod=trace cargo run -p kumod -- --policy simple_policy.lua

Contributing

Ensure that the code is formatted before submitting a PR.

You need to install StyLua to format lua:

$ cargo install stylua --features lua54

Then you can format both the rust and the lua code:

$ make fmt

Docker build

To build a lightweight alpine-based docker image:

$ ./ci/build-docker-image.sh
...
$ sudo docker image ls kumomta/smtpd
REPOSITORY      TAG       IMAGE ID       CREATED         SIZE
kumomta/smtpd   latest    962d8f453c6b   8 minutes ago   22MB

You can then run that image; this invocation mounts the kumo src dir at /config and then the KUMO_POLICY environment variable is used to override the default /config/policy.lua path to use the SMTP sink policy script sink.lua, which will accept and discard all mail:

$ sudo docker run --rm -p 2025:25 \
    -v .:/config \
    --name kumo-sink \
    --env KUMO_POLICY="/config/sink.lua" \
    kumomta/smtpd

Fuzzing

Some components have fuzzer coverage. To run it, follow the setup from the Rust Fuzz Book

Then:

$ cd crates/rfc5321/
$ cargo +nightly fuzz run parser