Selfhosted email delivery with postfix

Note that it is assumed that a Gitlab docker instance is setup on a Debian 10/11 machine... This article follows the post.

According to the docs, the official image of Gitlab doesn't include a Mail Transfer Agent (MTA) preinstalled. For our purposes this is the program that routes out the email from our system. So we'll install it on the host system and setup Gitlab to route mail to it.

This is simple enough, but getting our local hosted email service to play nice with Gmail is a different story.

We begin by setting up basic postfix email. Install postfix as per this. We only need step one.

To test:

echo "Subject: test" | sendmail -v mymail@mydomain.com

This will not actually deliver the mail as yet; but atleast it should run without errors!

To allow the docker container to access postfix we make a small change to /etc/postfix/main.cf. Add 0.0.0.0/0 to mynetworks. This allows any IP to initiate email, as IP address change with every container restarts, we will take this approach.

Remember to restart postfix on every edit to this file by:

sudo systemctl reload postfix

Then add this smtp settings in our Gitlab's docker-compose.yml:

gitlab_rails['smtp_enable'] = true
gitlab_rails['smtp_address'] = "gitlab.example.com"
gitlab_rails['smtp_port'] = 25

Note that 'smtp_address' will be the FQDN that we set as our host machine domain.

Now to test, execute the following:

sudo docker exec -it  gitlab-compose-web-1 bash
gitlab-rails console -e production

Notify.test_email('mymail@mydomain.com', 'Message Subject', 'Message Body').deliver_now

In the first command gitlab-compose-web-1 is the name of the container. To check your running name run sudo docker ps.

Note this will not yet work if you're using a Gmail addresses read on to fix this...

Setting up SASL (for Gmail receipients)#

Next thing to do is to install Dovecot. On debian:

sudo apt install dovecot-core dovecot-pop3d dovecot-imapd

Then in /etc/dovecot/conf.d/10-master.conf:

service auth {
  unix_listener auth-userdb {
    mode = 0666
    user = postfix
    group = postfix
  }

  # Postfix smtp-auth
  #unix_listener /var/spool/postfix/private/auth {
  #  mode = 0666
  #}

  # Auth process is run as this user.
  #user = $default_internal_user
}

Don't forget to restart dovecot:

sudo systemctl restart dovecot

Then modify postfix to use dovecot ADD /etc/postfix/main.cf:

smtpd_sasl_type = dovecot

Don't forget to restart postfix:

sudo systemctl reload postfix

Lastly we need to add a TXT record for our domain:

v=spf1 ip4:x.x.x.x ~all

where x.x.x.x is the IP of the server.

Now try:

echo "Subject: test" | sendmail -v me@gmail.com

Tip: handy commands to view the log messages: postfix: sudo tail -f /var/log/mail.log Dovecot: sudo tail -f /var/log/syslog