Postfix to sendgrid mail relay

Very simple mail relay, just set the APIKEY environment variable and you should be good to go.

This Docker image automatically updates whenever there is an update to the underlying Alpine image and/or Postfix is updated in the Alpine package repository. (See https://github.com/marius/postfix-sendgrid/actions for how this is implemented)

Heavily inspired by alterrebe/docker-mail-relay and simenduev/postfix-relay.

Warning

This assumes the host is running behind a firewall, you probably don't want to run this container exposed to the internet.

Docker run

docker run -d -e APIKEY=YOUR_KEY -p 25:25 ghcr.io/marius/postfix-sendgrid

Docker compose

  mailrelay:
    image: ghcr.io/marius/postfix-sendgrid
    environment:
      APIKEY: YOUR_KEY
    ports:
      - "25:25"

Using a secret:

secrets:
  sendgrid_apikey:
    file: /tank/docker/secrets/sendgrid_apikey

services:
  mailrelay:
    image: ghcr.io/marius/postfix-sendgrid
    environment:
      APIKEY_FILE: /run/secrets/sendgrid_apikey
    ports:
      - "25:25"
    secrets:
      - sendgrid_apikey

Testing

On the host:

ruby -r net/smtp -e 'Net::SMTP.start("localhost") { |s| s.send_mail "From: from@example.com\r\n\r\nHello via sendgrid", "from@example.com", "you@example.com" }'

From another container:

host# docker run -it --rm --add-host host.docker.internal:host-gateway ubuntu
container# apt update && apt install ruby -y
container# ruby -r net/smtp -e 'Net::SMTP.start("host.docker.internal") { |s| s.send_mail "From: from@example.com\r\n\r\nHello via sendgrid", "from@example.com", "you@example.com" }'

Sending email from other containers

Example Watchtower docker compose config

  watchtower:
    image: containrrr/watchtower
    environment:
      WATCHTOWER_NOTIFICATIONS: email
      WATCHTOWER_NOTIFICATION_EMAIL_TO: you@example.com
      WATCHTOWER_NOTIFICATION_EMAIL_FROM: watchtower@example.com
      WATCHTOWER_NOTIFICATION_EMAIL_SERVER: host.docker.internal
      WATCHTOWER_NOTIFICATION_EMAIL_SERVER_TLS_SKIP_VERIFY: "true"
      WATCHTOWER_NOTIFICATION_EMAIL_DELAY: 120
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    extra_hosts:
      - host.docker.internal:host-gateway

The delay is important, otherwise Watchtower might not be able to send emails.