This provides an SMTP Service which posts any e-mail it receives to an HTTP endpoint. The primary use case is for Ruby on Rails' ActionMailbox.

It can be used e.g. as a Transport behind a Relay Domain behind a real mail server like Mailcow. No guarantees are made when used directly on the public internet. There's no filtering nor authentication... but PRs are welcome.

Source: https://github.com/bb/action-mailbox-docker-relay

Docker Hub: https://hub.docker.com/r/bock/action-mailbox-docker-relay

Environment

• INGRESS_PASSWORD (required): the password which should be used to authenticate to the Rails application.
• URL (required): the URL which the e-mails should be posted to, e.g. https://example.org/rails/action_mailbox/relay/inbound_emails.
• HOSTS (optional, default: 0.0.0.0): the host or hosts (comma separated) which the server should bind to.
• PORTS (optional, default: 2525): the port or ports (comma separated) which the server should listen on.
• LOG_LEVEL (optional, default: WARN, fallback to DEBUG if unknown, case-insensitive): see https://rubyapi.org/o/logger
  • ERROR: only failures printed to stdout
  • WARN: messages on startup, shutdown, transient errors
  • INFO: one line per mail processed
  • DEBUG: everything

Example Docker Compose file

Essentials

Be sure to change the ingress password!

services:
  example-mailbox:
    image: bock/action-mailbox-docker-relay
    environment:
      URL: https://example.org/rails/action_mailbox/relay/inbound_emails
      INGRESS_PASSWORD: secr3t

Using mailcow network

Add it to mailcow under Admin -> Routing -> Transport Maps. Destination: e.g. example.org Next hop: e.g. example-mailbox:2525 Username/Password not needed.

services:
  example-mailbox:
    image: bock/action-mailbox-docker-relay
    environment:
      URL: https://example.org/rails/action_mailbox/relay/inbound_emails
      INGRESS_PASSWORD: secr3t
  networks:
    - mailcowdockerized_mailcow-network

networks:
  mailcowdockerized_mailcow-network:
    external: true

Using a template for multiple containers

x-base: &base
  image: bock/action-mailbox-docker-relay
  networks:
    - mailcowdockerized_mailcow-network

services:
  example-mailbox:
    <<: *base
    environment:
      URL: https://example.org/rails/action_mailbox/relay/inbound_emails
      INGRESS_PASSWORD: secr3t

  examplecom-mailbox:
    <<: *base
    environment:
      URL: https://www.example.com/rails/action_mailbox/relay/inbound_emails
      INGRESS_PASSWORD: secr3t
      # staging: Passwort sowohl in der Instanz als auch in Caddy basicauth

networks:
  mailcowdockerized_mailcow-network:
    external: true

Public (use at your own risk)

services:
  example-mailbox:
    image: bock/action-mailbox-docker-relay
    environment:
      URL: https://example.org/rails/action_mailbox/relay/inbound_emails
      INGRESS_PASSWORD: secr3t
      PORTS: 25
    ports:
      - "0.0.0.0:25:25

Alternative approaches

You do not need this, if you use an external email provider which provides webhooks like those described in the Action Mailer Basics Rails Guide (Mailgun, Mandrill, Postmark, Sendgrid).

You do not need this, if you run and configure your own mail server like those described in the Action Mailer Basics Rails Guide (Exim, Postfix, Qmail).

You do not need this, if you use Amazon SES/SNS. In this case you can use other 3rd party integrations like action_mailbox_amazon_ingress.

Action-mailbox-docker-postfix-relay by Loumaris / Christian Heimke provides roughly the same features, however you must build the Docker images yourself as the configuration will be hardcoded. It runs a full Postfix server and contains a minimal Rails app while this project only runs a single Ruby executable which receives the Mail and triggers the webhook. Their Docker image size on disk is ~675 MB while this is <100 MB.

PostalServer allows receiving e-mail by HTTP, however you'll need a custom Action Mailbox ingress to process their raw message payload.

mail_room gem allows polling IMAP mailboxes, so you could use it with GMail. It also works with Outlook / Hotmail.