Set up Postfix for incoming email

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This document takes you through the steps of setting up a basic Postfix mail server with IMAP authentication on Ubuntu, to be used with incoming email.

The instructions make the assumption that you are using the email address incoming@gitlab.example.com, that is, username incoming on host gitlab.example.com. Don’t forget to change it to your actual host when executing the example code snippets.

Configure your server firewall

  1. Open up port 25 on your server so that people can send email into the server over SMTP.
  2. If the mail server is different from the server running GitLab, open up port 143 on your server so that GitLab can read email from the server over IMAP.

Install packages

  1. Install the postfix package if it is not installed already: 

    sudo apt-get install postfix

    When asked about the environment, select ‘Internet Site’. When asked to confirm the hostname, make sure it matches gitlab.example.com.

  2. Install the mailutils package. 

    sudo apt-get install mailutils

Create user

  1. Create a user for incoming email. 

    sudo useradd -m -s /bin/bash incoming

  2. Set a password for this user. 

    sudo passwd incoming

    Be sure not to forget this, you will need it later.

Test the out-of-the-box setup

  1. Connect to the local SMTP server: 

    telnet localhost 25

    You should see a prompt like this: 

    Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 gitlab.example.com ESMTP Postfix (Ubuntu)

    If you get a Connection refused error instead, verify that postfix is running: 

    sudo postfix status

    If it is not, start it: 

    sudo postfix start

  2. Send the new incoming user an email to test SMTP, by entering the following into the SMTP prompt: 

    ehlo localhost
mail from: root@localhost
rcpt to: incoming@localhost
data
Subject: Re: Some issue

Sounds good!
.
quit
    note
    The . is a literal period on its own line.

    If you receive an error after entering rcpt to: incoming@localhost then your Postfix my_network configuration is not correct. The error will say ‘Temporary lookup failure’. See Configure Postfix to receive email from the Internet.

  3. Check if the incoming user received the email: 

    su - incoming
mail

    You should see output like this: 

    "/var/mail/incoming": 1 message 1 unread
>U   1 root@localhost                           59/2842  Re: Some issue

    Quit the mail app: 

    q

  4. Sign out of the incoming account, and go back to being root: 

    logout

Configure Postfix to use Maildir-style mailboxes

Courier, which we install later to add IMAP authentication, requires mailboxes to have the Maildir format, rather than mbox.

  1. Configure Postfix to use Maildir-style mailboxes: 

    sudo postconf -e "home_mailbox = Maildir/"

  2. Restart Postfix: 

    sudo /etc/init.d/postfix restart

  3. Test the new setup:

    1. Follow steps 1 and 2 of Test the out-of-the-box setup.

    2. Check if the incoming user received the email: 

      su - incoming
MAIL=/home/incoming/Maildir
mail

      You should see output like this: 

      "/home/incoming/Maildir": 1 message 1 unread
>U   1 root@localhost                           59/2842  Re: Some issue

      Quit the mail app: 

      q

    If mail returns an error Maildir: Is a directory then your version of mail doesn’t support Maildir style mailboxes. Install heirloom-mailx by running sudo apt-get install heirloom-mailx. Then, try the above steps again, substituting heirloom-mailx for the mail command.

  4. Sign out of the incoming account, and go back to being root: 

    logout

Install the Courier IMAP server

  1. Install the courier-imap package: 

    sudo apt-get install courier-imap

    And start imapd: 

    imapd start

  2. The courier-authdaemon isn’t started after installation. Without it, IMAP authentication fails: 

    sudo service courier-authdaemon start

    You can also configure courier-authdaemon to start on boot: 

    sudo systemctl enable courier-authdaemon

Configure Postfix to receive email from the internet

  1. Let Postfix know about the domains that it should consider local: 

    sudo postconf -e "mydestination = gitlab.example.com, localhost.localdomain, localhost"

  2. Let Postfix know about the IPs that it should consider part of the LAN:

    Let’s assume 192.168.1.0/24 is your local LAN. You can safely skip this step if you don’t have other machines in the same local network. 

    sudo postconf -e "mynetworks = 127.0.0.0/8, 192.168.1.0/24"

  3. Configure Postfix to receive mail on all interfaces, which includes the internet: 

    sudo postconf -e "inet_interfaces = all"

  4. Configure Postfix to use the + delimiter for sub-addressing: 

    sudo postconf -e "recipient_delimiter = +"

  5. Restart Postfix: 

    sudo service postfix restart

Test the final setup

  1. Test SMTP under the new setup:

    1. Connect to the SMTP server: 

      telnet gitlab.example.com 25

      You should see a prompt like this: 

      Trying 123.123.123.123...
Connected to gitlab.example.com.
Escape character is '^]'.
220 gitlab.example.com ESMTP Postfix (Ubuntu)

      If you get a Connection refused error instead, make sure your firewall is set up to allow inbound traffic on port 25.

    2. Send the incoming user an email to test SMTP, by entering the following into the SMTP prompt: 

      ehlo gitlab.example.com
mail from: root@gitlab.example.com
rcpt to: incoming@gitlab.example.com
data
Subject: Re: Some issue

Sounds good!
.
quit
      note
      The . is a literal period on its own line.

    3. Check if the incoming user received the email: 

      su - incoming
MAIL=/home/incoming/Maildir
mail

      You should see output like this: 

      "/home/incoming/Maildir": 1 message 1 unread
>U   1 root@gitlab.example.com                           59/2842  Re: Some issue

      Quit the mail app: 

      q

    4. Sign out of the incoming account, and go back to being root: 

      logout

  2. Test IMAP under the new setup:

    1. Connect to the IMAP server: 

      telnet gitlab.example.com 143

      You should see a prompt like this: 

      Trying 123.123.123.123...
Connected to mail.gitlab.example.com.
Escape character is '^]'.
- OK [CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE ACL ACL2=UNION] Courier-IMAP ready. Copyright 1998-2011 Double Precision, Inc.  See COPYING for distribution information.

    2. Sign in as the incoming user to test IMAP, by entering the following into the IMAP prompt: 

      a login incoming PASSWORD

      Replace PASSWORD with the password you set on the incoming user earlier.

      You should see output like this: 

      a OK LOGIN Ok.

    3. Disconnect from the IMAP server: 

      a logout

Done

If all the tests were successful, Postfix is all set up and ready to receive email! Continue with the incoming email guide to configure GitLab.

This document was adapted from https://help.ubuntu.com/community/PostfixBasicSetupHowto, by contributors to the Ubuntu documentation wiki.