SMTP Endpoint

Lumail exposes an SMTP submission endpoint for tools that cannot call the HTTP API directly. It is intended for low-volume transactional email such as auth codes, magic links, password resets, and operational messages.

If you are setting this up for an organization, start with the SMTP transactional email tutorial. It covers verified domains, API tokens, provider settings, and test sends.

For systems that support HTTP hooks, prefer POST /api/v1/emails. The HTTP API has a clearer request/response model and is easier to debug. The SMTP endpoint exists for compatibility with SMTP-only providers.

Under the hood, the SMTP endpoint is a thin adapter: it authenticates with your Lumail API token, parses the SMTP/MIME message, then forwards the request to POST /api/v1/emails. The HTTP API remains responsible for token validation, verified sending-domain checks, quotas, and priority queueing.

Connection Settings

Setting	Value
Host	smtp.lumail.io
Port	587
Security	STARTTLS
Username	Any non-empty value, for example your org slug
Password	A Lumail API token from Settings -> API Tokens

The username is used as a log label. The password must be a Lumail API token. The From address must use a verified Lumail sending domain in the same organization as the API token.

Priority

SMTP messages are treated as transactional by default. They are queued on Lumail's transactional priority QStash lane, separate from campaign and newsletter batches.

The default queue lane capacity is 40 emails per second for priority messages and 40 emails per second for bulk campaign messages. This separation prevents a large newsletter send from blocking OTP or magic-link delivery.

Message Rules

Rule	Default
Recipients	1 recipient per SMTP message
Attachments	Rejected
Size limit	1 MB
Tracking	Link and open tracking disabled by default
Content	HTML is preserved when present; otherwise text is sent as Markdown