docker-mailserver/docs/content/tutorials/installation-examples.md

Building a simple mailserver

WARNING: Adding the docker network's gateway to the list of trusted hosts, e.g. using the network or connected-networks option, can create an open relay, for instance if IPv6 is enabled on the host machine but not in Docker. (#1405)

We are going to use this docker based mailserver:

• First create a directory for the mailserver and get the setup script:

  mkdir -p /var/ds/mail.example.org
  cd /var/ds/mail.example.org/
  
  curl -o setup.sh \
      https://raw.githubusercontent.com/tomav/docker-mailserver/master/setup.sh
  chmod a+x ./setup.sh
  

• Create the file docker-compose.yml with a content like this:

  version: '2'
  
  services:
    mail:
      image: tvial/docker-mailserver:latest
      hostname: mail
      domainname: example.org
      container_name: mail
      ports:
      - "25:25"
      - "587:587"
      - "465:465"
      volumes:
      - ./data/:/var/mail/
      - ./state/:/var/mail-state/
      - ./config/:/tmp/docker-mailserver/
      - /var/ds/wsproxy/letsencrypt/:/etc/letsencrypt/
      environment:
      - PERMIT_DOCKER=network
      - SSL_TYPE=letsencrypt
      - ONE_DIR=1
      - DMS_DEBUG=1
      - SPOOF_PROTECTION=0
      - REPORT_RECIPIENT=1
      - ENABLE_SPAMASSASSIN=0
      - ENABLE_CLAMAV=0
      - ENABLE_FAIL2BAN=1
      - ENABLE_POSTGREY=0
      cap_add:
      - NET_ADMIN
      - SYS_PTRACE
  

  For more details about the environment variables that can be used, and their meaning and possible values, check also these:

  • https://github.com/tomav/docker-mailserver#environment-variables
  • https://github.com/tomav/docker-mailserver/blob/master/.env.dist

  Make sure to set the proper domainname that you will use for the emails. We forward only SMTP ports (not POP3 and IMAP) because we are not interested in accessing the mailserver directly (from a client). We also use these settings:

  • PERMIT_DOCKER=network because we want to send emails from other docker containers.
  • SSL_TYPE=letsencrypt because we will manage SSL certificates with letsencrypt.

• We need to open these ports on the firewall: 25, 587, 465

  ufw allow 25
  ufw allow 587
  ufw allow 465
  

  On your server you may have to do it differently.

• Pull the docker image:

  docker pull tvial/docker-mailserver:latest
  

• Now generate the DKIM keys with ./setup.sh config dkim and copy the content of the file config/opendkim/keys/domain.tld/mail.txt on the domain zone configuration at the DNS server. I use bind9 for managing my domains, so I just paste it on example.org.db:

  mail._domainkey IN      TXT     ( "v=DKIM1; h=sha256; k=rsa; "
          "p=MIIBIjANBgkqhkiG9w0BAQEFACAQ8AMIIBCgKCAQEAaH5KuPYPSF3Ppkt466BDMAFGOA4mgqn4oPjZ5BbFlYA9l5jU3bgzRj3l6/Q1n5a9lQs5fNZ7A/HtY0aMvs3nGE4oi+LTejt1jblMhV/OfJyRCunQBIGp0s8G9kIUBzyKJpDayk2+KJSJt/lxL9Iiy0DE5hIv62ZPP6AaTdHBAsJosLFeAzuLFHQ6USyQRojefqFQtgYqWQ2JiZQ3"
          "iqq3bD/BVlwKRp5gH6TEYEmx8EBJUuDxrJhkWRUk2VDl1fqhVBy8A9O7Ah+85nMrlOHIFsTaYo9o6+cDJ6t1i6G1gu+bZD0d3/3bqGLPBQV9LyEL1Rona5V7TJBGg099NQkTz1IwIDAQAB" )  ; ----- DKIM key mail for example.org
  
  

• Add these configurations as well on the same file on the DNS server:

  mail      IN  A   10.11.12.13
  
  ; mailservers for example.org
      3600  IN  MX  1  mail.example.org.
  
  ; Add SPF record
            IN TXT "v=spf1 mx ~all"
  

  Then don't forget to change the serial number and to restart the service.

• Get an SSL certificate from letsencrypt. I use wsproxy for managing SSL letsencrypt certificates of my domains:

  cd /var/ds/wsproxy
  ds domains-add mail mail.example.org
  ds get-ssl-cert myemail@gmail.com mail.example.org --test
  ds get-ssl-cert myemail@gmail.com mail.example.org
  

  Now the certificates will be available on /var/ds/wsproxy/letsencrypt/live/mail.example.org.

• Start the mailserver and check for any errors:

  apt install docker-compose
  docker-compose up mail
  

• Create email accounts and aliases with SPOOF_PROTECTION=0:

  ./setup.sh email add admin@example.org passwd123
  ./setup.sh email add info@example.org passwd123
  ./setup.sh alias add admin@example.org myemail@gmail.com
  ./setup.sh alias add info@example.org myemail@gmail.com
  ./setup.sh email list
  ./setup.sh alias list
  

  Aliases make sure that any email that comes to these accounts is forwarded to my real email address, so that I don't need to use POP3/IMAP in order to get these messages. Also no anti-spam and anti-virus software is needed, making the mailserver lighter.

• Or create email accounts and aliases with SPOOF_PROTECTION=1:

  ./setup.sh email add admin.gmail@example.org passwd123
  ./setup.sh email add info.gmail@example.org passwd123
  ./setup.sh alias add admin@example.org admin.gmail@example.org
  ./setup.sh alias add info@example.org info.gmail@example.org
  ./setup.sh alias add admin.gmail@example.org myemail@gmail.com
  ./setup.sh alias add info.gmail@example.org myemail@gmail.com
  ./setup.sh email list
  ./setup.sh alias list
  

  This extra step is required to avoid the 553 5.7.1 Sender address rejected: not owned by user error (the account used for setting up gmail is admin.gmail@example.org and info.gmail@example.org )

• Send some test emails to these addresses and make other tests. Then stop the container with Ctrl+c and start it again as a daemon: docker-compose up -d mail.

• Now save on Moodle configuration the SMTP settings and test by trying to send some messages to other users:

  • SMTP hosts: mail.example.org:465
  • SMTP security: SSL
  • SMTP username: info@example.org
  • SMTP password: passwd123