---
title: Mailboxes
description: "Connect sender accounts, providers, and how they are assigned to workers."
---

A mailbox is a sender account you connect to Warmbly. Every warmup message and campaign email goes out through one you own.

## Connecting an account

Open **Accounts** and choose **Add account**.

| Provider | Method | Notes |
|----------|--------|-------|
| Gmail / Google Workspace | OAuth (`gmail`) | Recommended. No password stored. Sends and syncs over the Gmail API |
| Outlook / Microsoft 365 | OAuth (`outlook`) | Recommended. No password stored. Runs on Microsoft Graph |
| Any other server | IMAP + SMTP (`smtp_imap`) | Custom domains, self-hosted, or providers without OAuth |

**OAuth** sends you to your provider's consent screen and returns a token instead of a password. Both OAuth providers use the provider's native API, never IMAP or SMTP, so consent asks to send mail and to read and organize your mailbox. It survives password changes and needs no app passwords or server settings.

**IMAP / SMTP** needs host, port, username, and password for each direction:

```text
SMTP   host: smtp.yourprovider.com   port: 465   username: you@yourdomain.com
IMAP   host: imap.yourprovider.com   port: 993   username: you@yourdomain.com
```

With two-factor authentication on, generate an app password in your provider's security settings and use that.

<Callout type="warn" title="Authentication runs on connect">
  Credentials and both connections are validated when you add the account, so wrong settings fail immediately rather than silently at send time. Tokens and credentials are sealed with envelope encryption before they touch storage.
</Callout>

**Limits**: `200` mailboxes per workspace by default (higher allowances come through a reviewed limit-increase request), and `5` new mailboxes per workspace per day as an abuse guardrail that resets daily. Spread large onboarding batches across days.

## What gets synced

Connecting a mailbox does two things: it imports the mailbox's recent history, and from then on it follows new mail as it arrives. Both are the same on every provider.

**The import** brings in the last `90` days, newest first, up to `5,000` messages per mailbox (the defaults; a self-hosted instance can change both under Instance settings). It reads the inbox, sent mail and archive (plus your own folders on Gmail and IMAP), and skips trash, drafts, spam and Gmail's "All Mail". You can watch it in the mailbox drawer's **Sync** card: a progress bar with a running count while it works, then "Up to date" with what was imported. Because it runs newest first, the mail you would look for is there within the first minute; a large mailbox finishes over the next while at a steady pace.

**Live sync** then follows every folder the provider exposes, including junk (so placement problems are visible) and sent mail (so a conversation shows both sides). Read state, flags, deletions and moves are mirrored too.

<Callout type="info" title="Fair use, not a hard cap">
  There is a budget on how much new mail one mailbox stores per day (`2,000` by default) and how much a whole workspace stores per day (`25,000`), plus a short burst limit so a mailing-list storm cannot swamp the workers. Mail over a budget is not dropped: it waits on the server with the sync cursor held, and comes in when the window rolls. Replies to your own outreach have their own budget and are never held behind ordinary inbound mail. The drawer says "Waiting on the sync budget until ..." while this is happening, and the mailbox checks back less often until then.
</Callout>

Only two patterns deactivate a mailbox's sync, and both mean something is wrong upstream: a flood (thousands of new messages in a single hour, more than any real inbox produces) or exceeding the daily budget on three of the last seven days. The mailbox then shows the reason under **Needs attention**; fix what is delivering that volume into it, or ask your administrator to raise the budget, and reactivate it.

## Sending controls

Set these on the mailbox's **Settings** tab. They apply to the next scheduled send, not retroactively.

| Control | Default | Range |
|---------|---------|-------|
| Daily campaign cap | `50`/day | `0` to `100` |
| Minimum gap between sends | `600s` (10 minutes) | A hard floor, with jitter added on top |

The default of `50` is deliberately conservative. `30` to `50`/day is the normal safe band; a fresh mailbox should start at `10` to `20` and ramp. Raise the cap only for a mailbox with proven reputation and low complaint and bounce rates.

<Callout type="warn" title="Do not jump a new mailbox to a high cap">
  A new mailbox has no reputation. Sudden high volume from a cold inbox is one of the fastest ways to land in spam.
</Callout>

### Keeping a copy of sent mail

SMTP mailboxes get a **Keep a copy of sent mail** toggle, on by default. SMTP submission puts nothing in your own account, so without it a message Warmbly sends exists only in the recipient's inbox: it shows up in neither your mail client nor the unibox thread. With it on, Warmbly files each message in the mailbox's Sent folder as it goes out, flagged read and dated when it was sent.

Turn it off when your provider already saves its own copy of anything submitted over SMTP, which Gmail, Fastmail and Zoho do, or the folder ends up with two of every message. Gmail and Outlook mailboxes connected with OAuth never show the toggle: their APIs file the copy themselves. Warmup mail is never filed, since it would bury your real sent mail.

The same tab sets the **display name**, **reply-to** (empty uses the mailbox address), **signature** in plain text and HTML, and **tags** for grouping.

### Custom tracking domain

Open pixels and click links go out on a shared tracking host by default, which means their reputation is the sum of everyone else using it. Pointing a subdomain of the domain you send from at that host puts them on your own name instead.

Type the subdomain into **Custom tracking domain** in the mailbox's Settings tab. Warmbly shows the exact `CNAME` to add, with the value taken from the host this Warmbly install serves tracking on (on a self-hosted install, that is whatever the operator set `TRACKING_DOMAIN` to). Add the record at your DNS provider, then press **Save & verify**.

Verification resolves the record live and reports what it finds:

| What it says | What it means |
| --- | --- |
| **Verified** | The subdomain resolves to the tracking host. New sends use it. |
| No DNS record yet | The name does not exist. The record has not been added, or has not propagated; usually minutes, up to an hour. |
| Points at something else | The record exists but its value is another host. The message names what it found so you can compare it with what you typed. |
| Nothing to point at | This install has no tracking host configured. Nothing can verify until an operator sets `TRACKING_DOMAIN`. |

A provider that flattens `CNAME` records (ALIAS records, apex flattening, proxied records) still verifies: Warmbly compares the addresses when there is no `CNAME` to read.

Press **Check again** any time to re-resolve without changing the value. Warmbly also re-checks every custom tracking domain on its own, hourly, so a record that finishes propagating after you saved starts being used without you doing anything, and one that later stops pointing at the tracking host stops being used instead of quietly breaking every link.

Until it verifies, tracking falls back to the shared host, so an unverified domain never breaks sending: links keep working, they just are not on your name yet. Links already sent keep working after a change; new sends pick up the new domain.

## Warmup

New mailboxes should warm up before carrying campaign volume. Defaults are `10`/day starting volume, `+1`/day ramp, and a `40`/day ceiling.

Start, pause, resume, or stop from the mailbox's **Warmup** tab, or for several mailboxes at once from the Accounts selection bar. **Pausing keeps your ramp progress; stopping resets it**, so a restart begins at the base volume again.

Keep warmup running after campaigns begin rather than switching it off once a mailbox looks ready. See [Warmup](/guides/warmup/).

<Callout type="info" title="Warmup is a paid feature">
  The model still supports separate free and premium pools, but access is gated to paid workspaces today.
</Callout>

## Worker assignment

You never pick a worker. Warmbly assigns each mailbox to a sending worker automatically and can move it later. Workers are the machines that send and sync, so spreading mailboxes across them spreads sending across network identities and IPs.

| Workspace | Placement |
|-----------|-----------|
| Free / trial | Shared free-tier workers |
| Paid | Shared premium workers |
| Plans including dedicated workers | A dedicated worker bound to the workspace, allocated on demand, falling back to shared premium and retrying later |

Within a tier, Warmbly picks the least-loaded healthy worker with capacity rather than packing onto the first one. Each mailbox contributes a load weight, so a worker's planned volume tracks the sum of its mailboxes' budgets.

**Risk is segregated.** A degraded, risky, or quarantined mailbox is never placed on a clean worker beside trusted inboxes, so one struggling mailbox cannot drag down the reputation others depend on.

Mailboxes migrate automatically when a trial upgrades, a subscription ends, a workspace moves to or from a dedicated worker, or a risk band changes. No action needed.

## Health

The Accounts list groups mailboxes as **Healthy** (sending normally), **Warming** (ramping through warmup), or **Needs attention** (paused, failing, or not sending), each row showing a live state and score. A drop between refreshes notifies you rather than waiting to be noticed.

The detail drawer runs a live `SPF`, `DKIM`, and `DMARC` check on your sending domain. Confirm it is green before sending; major providers require alignment for bulk and cold mail. A domain that stays Failing eventually stops cold sending and warmup from every mailbox on it, so fix the records and press **Re-check** to clear it straight away. See [Deliverability](/guides/deliverability/) for the grace period and exactly what is stopped.

Underneath, health moves through `healthy`, `watch`, `throttled`, `quarantined`, and `blocked`. These feed warmup pool selection, which only picks healthy mailboxes as partners, so an unhealthy one can be lowered in volume, removed from the pool, or blocked entirely. A blocked mailbox shows the reason and any appeal option on the Warmup tab, and must requalify on a fresh probation sample rather than waiting out the clock.

<Callout type="info" title="Health protects the pool">
  These controls act earlier than the point where providers start penalizing senders. Low complaint rate and low spam placement matter more than maximum throughput.
</Callout>

## Related guides

<Cards>
  <Card title="Deliverability" href="/guides/deliverability/" />
  <Card title="Personalization & Expressions" href="/guides/expressions/" />
</Cards>
