Postfix-DOCKERIZED

A simple Postfix SMTP TLS relay docker Alpine Linux based image with no local authentication enabled (to be run in a secure LAN).

About Postfix

Disclaimer: I am just the maintainer of this docker container, I did not write the software. Visit the Official Homepage to thank the author(s)! :)

Info: I originally forked this repositofy from Juan Luis Baptiste. Thank you for your work! :)

What is Postfix? It is Wietse Venema's mail server that started life at IBM research as an alternative to the widely-used Sendmail program. After eight years at Google, Wietse continues to maintain Postfix.

Postfix attempts to be fast, easy to administer, and secure. The outside has a definite Sendmail-ish flavor, but the inside is completely different.

Official Website - https://www.postfix.org/

Docs - https://www.postfix.org/documentation.html

My Github Repository - https://github.com/Bleala/Postfix-DOCKERIZED

Docker Hub - https://hub.docker.com/r/bleala/postfix

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Image, Versions and Architecture

I built this image based on Alpine Linux.

There will always be two different versions:

Tag	Content
Latest	Contains the latest stable version
x.x.x	Contains the Postfix and Alpine versions mentioned at the bottom of the page and in the release notes

I am using semantic versioning for this image. For all supported architectures there are the following versioned tags:

• Major (1)
• Minor (1.0)
• Patch (1.0.0)
• Latest

There are also several platforms supported:

Platform:

• linux/amd64
• linux/386
• linux/arm64
• linux/arm/v6
• linux/arm/v7

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Usage

To start the container you can run the following:

docker run -d --name postfix -p "25:25"  \
        -e SMTP_SERVER=your.mail.server \
        -e SERVER_HOSTNAME=your.mail.server \
        bleala/postfix:latest

But since docker compose is easier to maintain, I'll give you a valid docker compose example:

version: "3.9"

networks:
  postfix:
    name: postfix
    driver: bridge

secrets:
  smtp_password:
    file: /path/to/your/secret/file/smtp_password

services:
  # Postfix SMTP Relay - Simple Postfix SMTP TLS relay docker alpine based image with no local authentication enabled (to be run in a secure LAN).
  # https://hub.docker.com/r/bleala/postfix
  # https://github.com/Bleala/Postfix-DOCKERIZED
  postfix:
    image: bleala/postfix:latest
    container_name: postfix
    hostname: postfix
    restart: unless-stopped
    security_opt:
      - no-new-privileges:true
    environment:
      # Mandatory: Server address of the SMTP server to use.
      SMTP_SERVER:
      # Optional: (Default value: 587) Port address of the SMTP server to use.
      SMTP_PORT: 
      # Optional: Username to authenticate with.
      SMTP_USERNAME:
      # Optional (Mandatory if SMTP_USERNAME is set): Password of the SMTP user. (Not needed if SMTP_PASSWORD_FILE is used)
      SMTP_PASSWORD:
      # Mandatory: Server hostname for the Postfix container. Emails will appear to come from the hostname's domain.
      SERVER_HOSTNAME:
      # Optional: This will add a header for tracking messages upstream. Helpful for spam filters. Will appear as "RelayTag: ${SMTP_HEADER_TAG}" in the email headers.
      SMTP_HEADER_TAG:
      # Optional: Setting this will allow you to add additional, comma seperated, subnets to use the relay. Used like SMTP_NETWORKS='xxx.xxx.xxx.xxx/xx,xxx.xxx.xxx.xxx/xx'.
      SMTP_NETWORKS:
      # Optional: Set this to a mounted file containing the password, to avoid passwords in env variables.
      SMTP_PASSWORD_FILE:
      # Optional: Set this to yes to always add missing From:, To:, Date: or Message-ID: headers.
      ALWAYS_ADD_MISSING_HEADERS: yes
      # Optional: This will rewrite the from address overwriting it with the specified address for all email being relayed.
      OVERWRITE_FROM: "Your Name <[email protected]>"
      # Optional: This will use allow you to set a custom $mydestination value. Default is localhost.
      DESTINATION:
      # Optional: This will output the subject line of messages in the log.
      LOG_SUBJECT: yes
      # Optional: This will disable (no) or enable (yes) the use of SMTPUTF8
      SMTPUTF8_ENABLE: no
      # Optional: This will use allow you to set a custom $message_size_limit value. Default is 10240000.
      MESSAGE_SIZE_LIMIT:
    env_file:
      - .env
    networks:
      postfix:
    ports:
      - target: 25
        published: 25
        protocol: tcp
        mode: host
    secrets:
      - smtp_password
    volumes:
      - type: bind
        source: /etc/localtime
        target: /etc/localtime
        read_only: true

You can start the docker-compose.yml with the following command

docker compose up -d

If you want to see the container logs, you can run

docker compose logs -f

or

docker logs -f postfix

Google specifics

Gmail by default does not allow email clients that don't use OAUTH 2 for authentication (like Thunderbird or Outlook). First you need to enable access to "Less secure apps" on your google settings.

Also take into account that email From: header will contain the email address of the account being used to authenticate against the Gmail SMTP server (SMTP_USERNAME), the one on the email will be ignored by Gmail unless you add it as an alias.

Debugging

If you need troubleshooting the container you can set the environment variable DEBUG=yes for a more verbose output.

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Environment Variables

You can set fifteen different environment variables if you want to:

Variable	Info	Value
SMTP_SERVER	Server address of the SMTP server to use	Mandatory, default to unset
SERVER_HOSTNAME	Server hostname for the Postfix container Emails will appear to come from the hostname's domain	Mandatory, default to unset
SMTP_PORT	Port address of the SMTP server to use	Optional, default value is 587
SMTP_USERNAME	Username to authenticate with	Optional, default to unset
SMTP_PASSWORD	Password of the SMTP user If SMTP_PASSWORD_FILE is set, not needed	Mandatory, if SMTP_USERNAME is set Default to unset
SMTP_HEADER_TAG	This will add a header for tracking messages upstream Helpful for spam filters Will appear as "RelayTag: ${SMTP_HEADER_TAG}" in the email headers	Optional, default to unset
SMTP_NETWORKS	Setting this will allow you to add additional, comma seperated, subnets to use the relay Used like -e SMTP_NETWORKS='xxx.xxx.xxx.xxx/xx,xxx.xxx.xxx.xxx/xx'	Optional, default to unset
SMTP_USERNAME_FILE	Setting this to a mounted file containing the username, to avoid usernames in env variables Used like -e SMTP_USERNAME_FILE=/secrets/smtp_username	Optional, default to unset
SMTP_PASSWORD_FILE	Setting this to a mounted file containing the username, to avoid usernames in env variables Used like -e SMTP_PASSWORD_FILE=/secrets/smtp_username	Optional, default to unset
ALWAYS_ADD_MISSING_HEADERS	This is related to the always_add_missing_headers Postfix option If set to yes, Postfix will always add missing headers among From:, To:, Date: or Message-ID:	Optional, default to no
OVERWRITE_FROM	This will rewrite the from address overwriting it with the specified address for all email being relayed Example settings: OVERWRITE_FROM=[email protected] OVERWRITE_FROM="Your Name" [email protected]	Optional, default to unset
DESTINATION	This will define a list of domains from which incoming messages will be accepted	Optional, default to unset
LOG_SUBJECT	This will output the subject line of messages in the log	Optional, default to no
SMTPUTF8_ENABLE	This will enable or disable support for SMTPUTF8 Valid values are no to disable and yes to enable Not setting this variable will use the postfix default, which is yes.	Optional, default to yes
MESSAGE_SIZE_LIMIT	This will change the default limit of 10240000 bytes (10MB)	Optional, default to 10240000

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Build instructions

Clone this repo and then:

cd docker-Postfix
docker build -t bleala/postfix:dev .

Or you can use the provided docker-compose.yml file:

docker compose build

For more information on using multiple compose files see here. You can also find a prebuilt docker image from Docker Hub, which can be pulled with this command:

docker pull bleala/postfix:latest

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Versions

1.0.2 - 21.08.2024: Dependencies Update - Postfix 3.9.0, Alpine 3.20.2

1.0.1 - 07.06.2024: Packages Update - Postfix 3.8.6, Alpine 3.19.1

1.0.0 - 12.04.2024: Initial Version - Postfix 3.8.6, Alpine 3.19.1

Old Version History

1.0.0 - 12.04.2024: Initial Version - Postfix 3.8.6, Alpine 3.19.1

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Hope you enjoy it! :)

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