docker-compose.yml

version: '3'
services:
  smtp:
    image: namshi/smtp
    container_name: smtp_relay
    restart: always
    ports:
     - "25:25"
    environment:
     #  # MUST start with : e.g RELAY_NETWORKS: :192.168.0.0/24:10.0.0.0/16
     #  # if acting as a relay this or RELAY_DOMAINS must be filled out or incoming mail will be rejected
     #  RELAY_NETWORKS: :192.168.0.0/24
     #  # what domains should be accepted to forward to lower distance MX server.
     #  RELAY_DOMAINS: <domain1> : <domain2> : <domain3>
     #  # To act as a Gmail relay
     #  GMAIL_USER:
     #  GMAIL_PASSWORD:
     #  # For use with Amazon SES relay
     #  SES_USER:
     #  SES_PASSWORD:
     #  SES_REGION:
     #  # if provided will enable TLS support
     #  KEY_PATH:
     #  CERTIFICATE_PATH:
     #  # the outgoing mail hostname
     #  MAILNAME:
     #  # set this to any value to disable ipv6
     #  DISABLE_IPV6:
     # # Generic SMTP Relay
     # SMARTHOST_ADDRESS:
     # SMARTHOST_PORT:
     # SMARTHOST_USER:
     # SMARTHOST_PASSWORD:
     # SMARTHOST_ALIASES: