I run my mail server using docker, specifically the following images:

  * mailserver: https://github.com/tomav/docker-mailserver
  * webmail: https://github.com/jprjr/docker-rainloop

Combined in docker-compose:

  version: '2'
  
  services:
    mail:
      image: tvial/docker-mailserver:latest
      hostname: your_hostname
      domainname: your_domain
      environment:
        SSL_TYPE: letsencrypt
      ports:
      - "25:25"
      - "587:587"
      - "993:993"
      volumes:
      - ./data/mail:/var/mail
      - ./data/config/:/tmp/docker-mailserver/
      - /etc/letsencrypt/:/etc/letsencrypt
    rainloop:
      image: jprjr/rainloop
      environment:
        NGINX: 1
      ports:
        - 80:80
      volumes:
        - "./data/rainloop:/var/lib/rainloop/data"

The docker-compose.yml and postfix-accounts.cf files are the only configs you need for a basic setup.

See the projects on github, especially docker-mailserver for further info on complete features of this setup.