SMTP service

1. About

The Simple Mail Transfer Protocol (SMTP) is an internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages.

Note: The SMTP service is for servers and other equipment only, not for personal devices such as laptops and desktop computers which should use Microsoft Exchange.

2. Systems

2.1 Frontend


2.2 Backend

Always use the frontend DNS record

Never use the backend nodes directly:

  • backend may change without notice at any time (e.g. IP addresses, DNS records, configuration, etc.)
  • backend has no legacy support or grace periods, changes are implemented instantly
  • backend can be rebootet without notice at any time
  • backend access will soon be restricted

FQDN IPv6 IPv4 2a07:6b40::80 2a07:6b40::80
FQDN IPv6 IPv4 2a07:6b40::86 2a07:6b40::87 2a07:6b40::88 2a07:6b40::89

3. Features

3.1 Protocols

  • SMTP (TCP) on port 25

  • Submission over TLS (TCP) on port 465

  • Submission (TCP) on port 587

3.2 ACLs

  • mails are accepted from 2a07:6b40::/29, and only, everything else is denied (!= drop)

  • mails are relayed to mail servers with any ‘mail from’ and ‘rcpt to’ values

4. Operations

  • TODO

6. Backlog


  • n/a


  • regenerate containers with Debian 12

  • upgrade to current postfix and postfix defaults

  • provide enduser documentation

  • save logs somewhere for debugging/compliance reasons

  • load-balancing


  • anycasting instead of HA loadbalancing

  • test environment

  • benchmarking

Known issues

  • no known issues