Simple SMTP server Docker image

Table of Contents

• Quick reference
• Usage
  • Basic SMTP server
  • SMTP smart host
  • Environment variables

A debian slim image, which exim4. Forked from https://github.com/BytemarkHosting/docker-smtp.

But that one was not maintained, and didn’t run on arm (apple).

Quick reference

This image allows linked containers to send outgoing email. You can configure it to send email directly to recipients, or to act as a smart host that relays mail to an intermediate server (eg, GMail, SendGrid).

• Code repository: https://github.com/mmprogrami/smtp

• Where to file issues: https://github.com//mmprogrami/smtp/issues

• Maintained by: MMProgrami

• Supported architectures: Any architecture that has the Debian exim4-daemon-light package

Usage

Basic SMTP server

In this example, linked containers can connect to hostname mail and port 25 to send outgoing email. The SMTP container sends email out directly.

docker run --restart always --name mail -d bytemark/smtp

Via Docker Compose:

services:
  mail:
    image: ghcr.io/mmprogrami/smtp:1
    restart: always

SMTP smart host

In this example, linked containers can connect to hostname mail and port 25 to send outgoing email. The SMTP container acts as a smart host and relays mail to an intermediate server (eg, GMail, SendGrid).

docker run --restart always --name mail \
    -e RELAY_HOST=smtp.example.com \
    -e RELAY_PORT=587 \
    -e RELAY_USERNAME=alice@example.com \
    -e RELAY_PASSWORD=secretpassword \
    -d ghcr.io/mmprogrami/smtp:1

Via Docker Compose:

services:
  mail:
    image: ghcr.io/mmprogrami/smtp:1
    restart: always
    environment:
      RELAY_HOST: smtp.example.com
      RELAY_PORT: 587
      RELAY_USERNAME: alice@example.com
      RELAY_PASSWORD: secretpassword

Environment variables

All environment variables are optional. But if you specify a RELAY_HOST, then you’ll want to also specify the port, username and password otherwise it’s unlikely to work!

• MAILNAME: Sets Exim’s primary_hostname, which defaults to the hostname of the server.

• RELAY_HOST: The remote SMTP server address to use.

• RELAY_PORT: The remote SMTP server port to use.

• RELAY_USERNAME: The username to authenticate with the remote SMTP server.

• RELAY_PASSWORD: The password to authenticate with the remote SMTP server.

• RELAY_NETS: Declare which networks can use the smart host, separated by semi-colons. By default, this is set to 10.0.0.0/8;172.16.0.0/12;192.168.0.0/16, which provides a thin layer of protection in case port 25 is accidentally exposed to the public internet (which would make your SMTP container an open relay).