## 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**](https://en.wikipedia.org/wiki/Open_mail_relay), [for instance](https://github.com/tomav/docker-mailserver/issues/1405#issuecomment-590106498) if IPv6 is enabled on the host machine but not in Docker. ([#1405](https://github.com/tomav/docker-mailserver/issues/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](https://github.com/docker-scripts/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](https://github.com/docker-scripts/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`