docker-postfixrelay

Runs Postfix (as a relay) in Docker

• Source code: GitHub
• Docker container: Docker Hub
• Image base: Alpine Linux
• Init system: dumb-init
• Application: Postfix
• Architecture: linux/amd64,linux/arm64,linux/arm/v7

Explanation

• This runs Postfix (as a relay) in Docker.
• Most home ISPs block port 25, so outbound emails must be relayed through an external SMTP server (e.g., Gmail).
• This container acts as a single collections point for devices needing to send email.
• ⚠️ Postfix acts as an open relay. As such, this is not meant to be run on the internet, only on a trusted internal network! ⚠️

        Internal (LAN) network                                        Public internet

------------------
|                |
| Device sending |                            |   |
| email alert    | -------------              |   |
|                |             |              |   |
------------------             |              |   |
                               |              | F |
------------------             v              | i |
|                |       ------------------   | r |    -----------------------------       -------------------
| Device sending |       |                |   | e |    |                           |       |                 |
| email alert    | ----> | This container | --| w |--> | SMTP server (e.g., Gmail) | ----> | Recipient email |
|                |       |                |   | a |    |                           |       |                 |
------------------       ------------------   | l |    -----------------------------       -------------------
                               ^              | l |
------------------             |              |   |
|                |             |              |   |
| Device sending |             |              |   |
| email alert    | -------------              |   |
|                |
------------------

Requirements

• You must already have an account on an external SMTP server (e.g., Gmail, AWS SES, etc...).
• Your external SMTP server must be using encryption (i.e., plaintext is not allowed)

Docker image information

Docker image tags

• latest: Latest version
• X.X.X: Semantic version (use if you want to stick on a specific version)

Environment variables

Ports

Volumes

Example usage

Below is an example docker-compose.yml file.

version: '3'
services:
  postfixrelay:
    container_name: docker-postfixrelay
    restart: unless-stopped
    environment:
      - TZ=America/New_York
      - RELAY_HOST=smtp.gmail.com
      - RELAY_PORT=587
      # comment out if using secrets
      - RELAY_USER=your_email_here@gmail.com
      - RELAY_PASS=your_password_here
      # uncomment below if using secrets
      # - RELAY_USER_FILE=/run/secrets/RELAY_USER_FILE
      # - RELAY_PASS_FILE=/run/secrets/RELAY_PASS_FILE
      - RELAY_SUBMISSIONS=true
      - TEST_EMAIL=test_email@domain.com
      - TEST_EMAIL_SUBJECT=Destroy After Reading
      - MYORIGIN=domain.com
      - FROMADDRESS=my_email@domain.com
      - MYNETWORKS=1.2.3.4/24
      - MSG_SIZE=30720000
      - LOG_DISABLE=true
    # uncomment below if using secrets
    # secrets:
    #   - RELAY_USER_FILE
    #   - RELAY_PASS_FILE
    networks:
      - postfixrelay
    ports:
      - '25:25'
    volumes:
      - 'postfixrelay_data:/var/spool/postfix'
    image: loganmarchione/docker-postfixrelay:latest

networks:
  postfixrelay:

volumes:
  postfixrelay_data:
    driver: local

# uncomment below if using secrets
# secrets:
#    RELAY_USER_FILE:
#      file: ./relay_user.txt
#    RELAY_PASS_FILE:
#      file: ./relay_pass.txt

Debugging only

Below is an example of running locally (used to edit/test/debug).

# Build the Dockerfile
docker compose -f docker-compose-dev.yml up -d

# View logs
docker compose -f docker-compose-dev.yml logs -f

# Destroy when done
docker compose -f docker-compose-dev.yml down