GitLab can be set up to allow users to comment on issues and merge requests by replying to notification emails.
In order to do this, you need access to an IMAP-enabled email account, with a provider or server that supports [email sub-addressing](https://en.wikipedia.org/wiki/Email_address#Sub-addressing). Sub-addressing is a feature where any email to `user+some_arbitrary_tag@example.com` will end up in the mailbox for `user@example.com`, and is supported by providers such as Gmail, Yahoo! Mail, Outlook.com and iCloud, as well as the [Postfix](http://www.postfix.org/) mail server which you can run on-premises.
## Get a mailbox
If you want to use a Gmail with Reply by email, make sure you have [IMAP access enabled](https://support.google.com/mail/troubleshooter/1668960?hl=en#ts=1665018) and [allow less secure apps to access the account](https://support.google.com/accounts/answer/6010255).
Reply by email requires an IMAP-enabled email account, with a provider or server that supports [email sub-addressing](https://en.wikipedia.org/wiki/Email_address#Sub-addressing). Sub-addressing is a feature where any email to `user+some_arbitrary_tag@example.com` will end up in the mailbox for `user@example.com`, and is supported by providers such as Gmail, Yahoo! Mail, Outlook.com and iCloud, as well as the Postfix mail server which you can run on-premises.
To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these instructions](https://help.ubuntu.com/community/PostfixBasicSetupHowto).
If you want to use Gmail with Reply by email, make sure you have [IMAP access enabled](https://support.google.com/mail/troubleshooter/1668960?hl=en#ts=1665018) and [allow less secure apps to access the account](https://support.google.com/accounts/answer/6010255).
To set up a basic Postfix mail server with IMAP access on Ubuntu, follow [these instructions](./postfix.md).
This document will take you through the steps of setting up a basic Postfix mail server with IMAP authentication on Ubuntu, to be used with Reply by email.
The instructions make the assumption that you will be using the email address `replies@gitlab.example.com`, that is, username `replies` on host `gitlab.example.com`. Don't forget to change it to your actual host when executing the example code snippets.
## Configure your server DNS
1. Add an MX record pointing from `gitlab.example.com` to your server IP.
1. Add an A record pointing from `mail.gitlab.example.com` to your server IP.
1. Verify that the changes have propagated:
```sh
dig mx gitlab.example.com
```
```sh
dig a mail.gitlab.example.com
```
You should see an `ANSWER SECTION` with the expected result in the output for both.
## Install packages
1. Install the `postfix` package if it is not installed already:
```sh
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`.
1. Install the `mailutils` package.
```sh
sudo apt-get install mailutils
```
## Create user
1. Create a user for replies.
```sh
sudo useradd -m -s /bin/bash replies
```
1. Set a password for this user.
```sh
sudo passwd replies
```
Be sure not to forget this, you'll need it later.
## Test the out-of-the-box setup
1. Connect to the local SMTP server:
```sh
telnet localhost 25
```
You should see a prompt like this:
```sh
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, check if `postfix` is running:
```sh
sudo postfix status
```
If it is not, start it:
```sh
sudo postfix start
```
1. Send the new `replies` user a dummy email to test SMTP, by entering the following into the SMTP prompt:
```
ehlo localhost
mail from: root@localhost
rcpt to: replies@localhost
data
Subject: Re: Some issue
Sounds good!
.
quit
```
(Note: The `.` is a literal period on its own line)
1. Check if the `replies` user received the email:
```sh
sh - replies
mail
```
You should see output like this:
```
"/var/mail/replies": 1 message 1 unread
>U 1 root@localhost 59/2842 Re: Some issue
```
Quit the mail app:
```sh
q
```
1. Log out of the `replies` account and go back to being `root`:
```sh
logout
```
## Configure Postfix to use Maildir-style mailboxes
Courier, which we will install later to add IMAP authentication, requiers mailboxes to have the Maildir format, rather than mbox.
1. Configure Postfix to use Maildir-style mailboxes:
```sh
sudo postconf -e "home_mailbox = Maildir/"
sudo postconf -e "mailbox_command = "
```
1. Restart Postfix:
```sh
sudo postfix restart
```
1. Test the new setup:
1. Follow steps 1 and 2 of "Test the out-of-the-box setup".
2. Check if the `replies` user received the email:
```sh
sh - replies
MAIL=/home/replies/Maildir
mail
```
You should see output like this:
```
"/home/replies/Maildir": 1 message 1 unread
>U 1 root@localhost 59/2842 Re: Some issue
```
Quit the mail app:
```sh
q
```
1. Log out of the `replies` account and go back to being `root`:
```sh
logout
```
## Install the Courier IMAP server
1. Install the `courier-imap` package:
```sh
sudo apt-get install courier-imap
```
## Configure Postfix to receive email from the internet
1. Let Postfix know about the domains that it should consider local:
1. Configure Postfix to receive mail on all interfaces, which includes the internet:
```sh
sudo postconf -e "init_interfaces = all"
```
1. Configure Postfix to receive mail on both IPv4 and IPv6 protocols:
```sh
sudo postconf -e "inet_protocols = all"
```
## Test the final setup
1. Test SMTP under the new setup:
1. Connect to the SMTP server:
```sh
telnet mail.gitlab.example.com 25
```
You should see a prompt like this:
```sh
Trying 123.123.123.123...
Connected to mail.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 setup to allow inbound traffic on port 25.
1. Send the `replies` user a dummy email to test SMTP, by entering the following into the SMTP prompt:
```
ehlo gitlab.example.com
mail from: root@gitlab.example.com
rcpt to: replies@gitlab.example.com
data
Subject: Re: Some issue
Sounds good!
.
quit
```
(Note: The `.` is a literal period on its own line)
1. Check if the `replies` user received the email:
```sh
sh - replies
MAIL=/home/replies/Maildir
mail
```
You should see output like this:
```
"/home/replies/Maildir": 1 message 1 unread
>U 1 root@gitlab.example.com 59/2842 Re: Some issue
```
Quit the mail app:
```sh
q
```
1. Log out of the `replies` account and go back to being `root`:
```sh
logout
```
1. Test IMAP under the new setup:
1. Connect to the IMAP server:
```sh
telnet mail.gitlab.example.com 143
```
You should see a prompt like this:
```sh
Trying 123.123.123.123...
Connected to mail.example.gitlab.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.
```
1. Sign in as the `replies` user to test IMAP, by entering the following into the IMAP prompt:
```
a login replies PASSWORD
```
Replace PASSWORD by the password you set on the `replies` user earlier.
You should see output like this:
```
a OK LOGIN Ok.
```
1. Disconnect from the IMAP server:
```sh
a logout
```
## Done!
If all the tests went all right, Postfix is all set up and ready to receive email! Continue with the [Reply by email](./README.md) doc to configure GitLab.
---------
_This document was adapted from https://help.ubuntu.com/community/PostfixBasicSetupHowto, by contributors to the Ubuntu documentation wiki._
