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Basic Installation

Building a Simple Mail-Server

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.

We are going to use this docker based mailserver:

  • First create a directory for docker-mailserver to store data in, and get the setup.sh script:

    mkdir -p /var/ds/mail.example.com
cd /var/ds/mail.example.com/

curl -o setup.sh \
    https://raw.githubusercontent.com/docker-mailserver/docker-mailserver/master/setup.sh
chmod a+x ./setup.sh

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

    Example

    version: '3.8'

services:
  mailserver:
    image: docker.io/mailserver/docker-mailserver:latest
    container_name: mailserver
    hostname: mail
    domainname: example.com
    ports:
        - "25:25"
        - "587:587"
        - "465:465"
    volumes:
        - ./docker-data/dms/mail-data/:/var/mail/
        - ./docker-data/dms/mail-state/:/var/mail-state/
        - ./docker-data/dms/mail-logs/:/var/log/mail/
        - ./docker-data/dms/config/:/tmp/docker-mailserver/
        - /etc/localtime:/etc/localtime:ro
        - /var/ds/wsproxy/letsencrypt/:/etc/letsencrypt/
    environment:
        - PERMIT_DOCKER=network
        - SSL_TYPE=letsencrypt
        - ONE_DIR=1
        - DMS_DEBUG=0
        - 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:

    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 mail-server 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 ports 25, 587 and 465 on the firewall:

    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 mailserver/docker-mailserver:latest

  • Now generate the DKIM keys with ./setup.sh config dkim and copy the content of the file docker-data/dms/config/opendkim/keys/example.com/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.com.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.com

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

    mail      IN  A   10.11.12.13

; mail-server for example.com
    3600  IN  MX  1  mail.example.com.

; 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.com
ds get-ssl-cert external-account@gmail.com mail.example.com --test
ds get-ssl-cert external-account@gmail.com mail.example.com

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

  • Start docker-mailserver and check for any errors:

    apt install docker-compose
docker-compose up mailserver

  • Create email accounts and aliases with SPOOF_PROTECTION=0:

    ./setup.sh email add admin@example.com passwd123
./setup.sh email add info@example.com passwd123
./setup.sh alias add admin@example.com external-account@gmail.com
./setup.sh alias add info@example.com external-account@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 mail-server lighter.

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

    ./setup.sh email add admin.gmail@example.com passwd123
./setup.sh email add info.gmail@example.com passwd123
./setup.sh alias add admin@example.com admin.gmail@example.com
./setup.sh alias add info@example.com info.gmail@example.com
./setup.sh alias add admin.gmail@example.com external-account@gmail.com
./setup.sh alias add info.gmail@example.com external-account@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.com and info.gmail@example.com )

  • 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 mailserver.

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

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