Email: Outbound (Messages API → Brevo)¶
Outbound email takes two paths:
Path 1: Messages Backend → Brevo (Direct)¶
The Messages Django backend sends emails directly to Brevo, bypassing MTA-out:
MTA_OUT_MODE=relay
MTA_OUT_RELAY_HOST=smtp-relay.brevo.com:587
MTA_OUT_RELAY_USERNAME=<brevo-username>
MTA_OUT_RELAY_PASSWORD=<brevo-password>
MTA_OUT_SMTP_TLS_SECURITY_LEVEL=may
This avoids TLS issues with MTA-out's self-signed snakeoil certificate.
Path 2: Calendars → Messages API → Brevo¶
When a calendar is linked to a Messages mailbox, invitations use this path:
Calendars Backend → POST https://api.messages.<domain>/api/v1.0/submit/
(X-API-Key + X-Channel-Id authentication)
↓
Messages Backend → Brevo SMTP
This preserves the mailbox sender identity. The email appears to come from the user's mailbox address.
Why Not Through MTA-out?¶
MTA-out uses self-signed TLS certificates. The Python smtplib client (used by both backends) fails the TLS handshake:
Both backends connect directly to Brevo (port 587, proper TLS) instead.
Port Requirements¶
- Outbound port 25: NOT required (Brevo uses 587)
- Outbound port 587: Must be open (usually is by default)