Simple Postfix SMTP docker image with SASL and DKIM authentication.
It also includes syslog to enable logging to stdout.

docker run \
  -p 25:25 \
  -e MYHOSTNAME="mail.example.com" \
  -e MYDOMAIN="example.com" \
  -e INET_INTERFACE="all" \
  -e MYNETWORKS="172.16.0.0/12" \
  -e RELAYHOST="[172.16.0.1]" \
  -e TZ="Asia/Tokyo" \
  -e SASL_USER="test:foobar" \
  -e DKIM_KEY="dkim private key include LF" \
  actindi/postfix-sender:latest

Create a private key on other host.

opendkim-genkey -b 2048 -d example.com

Set private key to DKIM_KEY, and public key set to DNS.

• MYHOSTNAME: Postfix main.cf 'myhostname' setting. And SASL realm.
• MYDOMAIN: Postfix main.cf 'mydomain' setting. And OpenDKIM 'Domain' setting.
• INET_INTERFACE: Postfix main.cf 'inet_interface' setting.
• MYNETWORKS: Postfix main.cf 'mynetworks' setting.
• RELAYHOST: Postfix main.cf 'relayhost' setting.
• TZ?: time zone. default is UTC.
• SASL_USER?: If use SASL authentication, set 'user:password' format. Only one user.
• DKIM_KEY?: If use DKIM authentication, set RSA key.