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• latest, rocky8 (Rocky Linux) alma8 (AlmaLinux)
• centos8 (We have finished support for CentOS 8.)
• centos7

amd64, arm64(for Raspberry Pi)

FROM rockylinux:8  
MAINTAINER "Hiroki Takeyama"

ENV TIMEZONE Asia/Tokyo

ENV HOSTNAME smtp.example.com  
ENV DOMAIN_NAME example.com

ENV MESSAGE_SIZE_LIMIT 10240000

ENV AUTH_USER user  
ENV AUTH_PASSWORD password

ENV DISABLE_SMTP_AUTH_ON_PORT_25 true

ENV ENABLE_DKIM true  
ENV DKIM_KEY_LENGTH 1024  
ENV DKIM_SELECTOR default

# SSL Certificates  
VOLUME /ssl_certs
# DKIM Keys  
VOLUME /dkim_keys

# SMTP  
EXPOSE 25  
# Submission  
EXPOSE 587  
# SMTPS  
EXPOSE 465

You can send a mail using a secure connection (SSL/TLS).
In advance you may need to add SPF, DKIM, DMARC records to your DNS server in order that your mail avoids being marked as a spam.

version: '3'  
services:  
  postfix:  
    image: takeyamajp/postfix  
    ports:  
      - "8025:25"  
      - "8587:587"  
      - "8465:465"  
    volumes:  
      - /my/own/certs:/ssl_certs  
      - /my/own/keys:/dkim_keys  
    environment:  
      TIMEZONE: "Asia/Tokyo"  
      HOSTNAME: "smtp.example.com"  
      DOMAIN_NAME: "example.com"  
      MESSAGE_SIZE_LIMIT: "10240000"  
      AUTH_USER: "user"  
      AUTH_PASSWORD: "password"  
      DISABLE_SMTP_AUTH_ON_PORT_25: "true"  
      ENABLE_DKIM: "true"  
      DKIM_KEY_LENGTH: "1024"  
      DKIM_SELECTOR: "default"

You can use any time zone such as America/Chicago that can be used in Rocky Linux.

See below for zones.
https://www.unicode.org/cldr/charts/latest/verify/zones/en.html

The maximum size in bytes of a mail you can send. (attached files included)
Increase the value of MESSAGE_SIZE_LIMIT, if you send a mail of more than 10MB size.

The user name used at authentication will be a format like a e-mail address (e.g. [email protected]).
It won't be included in a sent mail, so you can use any sender address according to your purpose.

You can usually use submission port 587.
Use port 465 if your mail client needs SMTPS (SMTP over SSL), then ignore a displayed certificate warning.
Port 25 is disabled by default. Set DISABLE_SMTP_AUTH_ON_PORT_25 to false If you want to use it.

The self-signed certificate will be created automatically into the volume '/ssl_certs', and it can be added to your OS (e.g. Windows, Linux, iOS, and Android) as the root certificate in order to avoid warnings on your mail clients.

If you have valid server certificates, you can use them.
And if you also have the intermediate certificate, append after the server certificate.

cat server_cert.pem intermediate_CA.pem > cert.pem

The public key will be displayed on 'docker logs'.
Mount the volume '/dkim_keys' on your host machine. Otherwise the key will be changed every time this container starts.
You can set DKIM_KEY_LENGTH to 2048 if your DNS server supports TXT records of more than 255 length.
If you have a mail server besides this container, you will need to change DKIM_SELECTOR from 'default' so that it doesn't overlap with other one.

This container logs all failed and successful deliveries to 'docker logs'.

Use the following command to view the logs in real time.

docker logs -f postfix