gitlab-org--gitlab-foss/doc/administration/reply_by_email.md

# Reply by email

GitLab can be set up to allow users to comment on issues and merge requests by
replying to notification emails.

## Requirement

Reply by email requires an IMAP-enabled email account. GitLab allows you to use
three strategies for this feature:
- using email sub-addressing
- using a dedicated email address
- using a catch-all mailbox

### Email sub-addressing

**If your provider or server supports email sub-addressing, we recommend using it.
Some features (e.g. create new issue via email) only work with sub-addressing.**

[Sub-addressing](https://en.wikipedia.org/wiki/Email_address#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, Google Apps, Yahoo! Mail, Outlook.com and iCloud, as well as the Postfix
mail server which you can run on-premises.

### Dedicated email address

This solution is really simple to set up: you just have to create an email
address dedicated to receive your users' replies to GitLab notifications.

### Catch-all mailbox

A [catch-all mailbox](https://en.wikipedia.org/wiki/Catch-all) for a domain will
"catch all" the emails addressed to the domain that do not exist in the mail
server.

## How it works?

### 1. GitLab sends a notification email

When GitLab sends a notification and Reply by email is enabled, the `Reply-To`
header is set to the address defined in your GitLab configuration, with the
`%{key}` placeholder (if present) replaced by a specific "reply key". In
addition, this "reply key" is also added to the `References` header.

### 2. You reply to the notification email

When you reply to the notification email, your email client will:

- send the email to the `Reply-To` address it got from the notification email
- set the `In-Reply-To` header to the value of the `Message-ID` header from the
  notification email
- set the `References` header to the value of the `Message-ID` plus the value of
  the notification email's `References` header.

### 3. GitLab receives your reply to the notification email

When GitLab receives your reply, it will look for the "reply key" in the
following headers, in this order:

1. the `To` header
1. the `References` header

If it finds a reply key, it will be able to leave your reply as a comment on
the entity the notification was about (issue, merge request, commit...).

For more details about the `Message-ID`, `In-Reply-To`, and `References headers`,
please consult [RFC 5322](https://tools.ietf.org/html/rfc5322#section-3.6.4).

## Set it up

If you want to use Gmail / Google Apps with Reply by email, make sure you have
[IMAP access enabled](https://support.google.com/mail/troubleshooter/1668960?hl=en#ts=1665018)
and [allowed less secure apps to access the account](https://support.google.com/accounts/answer/6010255)
or [turn-on 2-step validation](https://support.google.com/accounts/answer/185839)
and use [an application password](https://support.google.com/mail/answer/185833).

To set up a basic Postfix mail server with IMAP access on Ubuntu, follow the
[Postfix setup documentation](reply_by_email_postfix_setup.md).

### Omnibus package installations

1. Find the `incoming_email` section in `/etc/gitlab/gitlab.rb`, enable the
  feature and fill in the details for your specific IMAP server and email account:

    ```ruby
    # Configuration for Postfix mail server, assumes mailbox incoming@gitlab.example.com
    gitlab_rails['incoming_email_enabled'] = true

    # The email address including the `%{key}` placeholder that will be replaced to reference the item being replied to.
    # The placeholder can be omitted but if present, it must appear in the "user" part of the address (before the `@`).
    gitlab_rails['incoming_email_address'] = "incoming+%{key}@gitlab.example.com"

    # Email account username
    # With third party providers, this is usually the full email address.
    # With self-hosted email servers, this is usually the user part of the email address.
    gitlab_rails['incoming_email_email'] = "incoming"
    # Email account password
    gitlab_rails['incoming_email_password'] = "[REDACTED]"

    # IMAP server host
    gitlab_rails['incoming_email_host'] = "gitlab.example.com"
    # IMAP server port
    gitlab_rails['incoming_email_port'] = 143
    # Whether the IMAP server uses SSL
    gitlab_rails['incoming_email_ssl'] = false
    # Whether the IMAP server uses StartTLS
    gitlab_rails['incoming_email_start_tls'] = false

    # The mailbox where incoming mail will end up. Usually "inbox".
    gitlab_rails['incoming_email_mailbox_name'] = "inbox"
    # The IDLE command timeout.
    gitlab_rails['incoming_email_idle_timeout'] = 60
    ```

    ```ruby
    # Configuration for Gmail / Google Apps, assumes mailbox gitlab-incoming@gmail.com
    gitlab_rails['incoming_email_enabled'] = true

    # The email address including the `%{key}` placeholder that will be replaced to reference the item being replied to.
    # The placeholder can be omitted but if present, it must appear in the "user" part of the address (before the `@`).
    gitlab_rails['incoming_email_address'] = "gitlab-incoming+%{key}@gmail.com"

    # Email account username
    # With third party providers, this is usually the full email address.
    # With self-hosted email servers, this is usually the user part of the email address.
    gitlab_rails['incoming_email_email'] = "gitlab-incoming@gmail.com"
    # Email account password
    gitlab_rails['incoming_email_password'] = "[REDACTED]"

    # IMAP server host
    gitlab_rails['incoming_email_host'] = "imap.gmail.com"
    # IMAP server port
    gitlab_rails['incoming_email_port'] = 993
    # Whether the IMAP server uses SSL
    gitlab_rails['incoming_email_ssl'] = true
    # Whether the IMAP server uses StartTLS
    gitlab_rails['incoming_email_start_tls'] = false

    # The mailbox where incoming mail will end up. Usually "inbox".
    gitlab_rails['incoming_email_mailbox_name'] = "inbox"
    # The IDLE command timeout.
    gitlab_rails['incoming_email_idle_timeout'] = 60
    ```
    
    ```ruby
    # Configuration for Microsoft Exchange mail server w/ IMAP enabled, assumes mailbox incoming@exchange.example.com
    gitlab_rails['incoming_email_enabled'] = true

    # The email address replies are sent to - Exchange does not support sub-addressing so %{key} is not used here
    gitlab_rails['incoming_email_address'] = "incoming@exchange.example.com"

    # Email account username
    # Typically this is the userPrincipalName (UPN)
    gitlab_rails['incoming_email_email'] = "incoming@ad-domain.example.com"
    # Email account password
    gitlab_rails['incoming_email_password'] = "[REDACTED]"

    # IMAP server host
    gitlab_rails['incoming_email_host'] = "exchange.example.com"
    # IMAP server port
    gitlab_rails['incoming_email_port'] = 993
    # Whether the IMAP server uses SSL
    gitlab_rails['incoming_email_ssl'] = true
    ```

1. Reconfigure GitLab for the changes to take effect:

    ```sh
    sudo gitlab-ctl reconfigure
    ```

1. Verify that everything is configured correctly:

    ```sh
    sudo gitlab-rake gitlab:incoming_email:check
    ```

1. Reply by email should now be working.

### Installations from source

1. Go to the GitLab installation directory:

    ```sh
    cd /home/git/gitlab
    ```

1. Find the `incoming_email` section in `config/gitlab.yml`, enable the feature
  and fill in the details for your specific IMAP server and email account:

    ```sh
    sudo editor config/gitlab.yml
    ```

    ```yaml
    # Configuration for Postfix mail server, assumes mailbox incoming@gitlab.example.com
    incoming_email:
      enabled: true

      # The email address including the `%{key}` placeholder that will be replaced to reference the item being replied to.
      # The placeholder can be omitted but if present, it must appear in the "user" part of the address (before the `@`).
      address: "incoming+%{key}@gitlab.example.com"

      # Email account username
      # With third party providers, this is usually the full email address.
      # With self-hosted email servers, this is usually the user part of the email address.
      user: "incoming"
      # Email account password
      password: "[REDACTED]"

      # IMAP server host
      host: "gitlab.example.com"
      # IMAP server port
      port: 143
      # Whether the IMAP server uses SSL
      ssl: false
      # Whether the IMAP server uses StartTLS
      start_tls: false

      # The mailbox where incoming mail will end up. Usually "inbox".
      mailbox: "inbox"
      # The IDLE command timeout.
      idle_timeout: 60
    ```

    ```yaml
    # Configuration for Gmail / Google Apps, assumes mailbox gitlab-incoming@gmail.com
    incoming_email:
      enabled: true

      # The email address including the `%{key}` placeholder that will be replaced to reference the item being replied to.
      # The placeholder can be omitted but if present, it must appear in the "user" part of the address (before the `@`).
      address: "gitlab-incoming+%{key}@gmail.com"

      # Email account username
      # With third party providers, this is usually the full email address.
      # With self-hosted email servers, this is usually the user part of the email address.
      user: "gitlab-incoming@gmail.com"
      # Email account password
      password: "[REDACTED]"

      # IMAP server host
      host: "imap.gmail.com"
      # IMAP server port
      port: 993
      # Whether the IMAP server uses SSL
      ssl: true
      # Whether the IMAP server uses StartTLS
      start_tls: false

      # The mailbox where incoming mail will end up. Usually "inbox".
      mailbox: "inbox"
      # The IDLE command timeout.
      idle_timeout: 60
    ```
    
    ```yaml
    # Configuration for Microsoft Exchange mail server w/ IMAP enabled, assumes mailbox incoming@exchange.example.com
    incoming_email:
      enabled: true

      # The email address replies are sent to - Exchange does not support sub-addressing so %{key} is not used here
      address: "incoming@exchange.example.com"

      # Email account username
      # Typically this is the userPrincipalName (UPN)
      user: "incoming@ad-domain.example.com"
      # Email account password
      password: "[REDACTED]"

      # IMAP server host
      host: "exchange.example.com"
      # IMAP server port
      port: 993
      # Whether the IMAP server uses SSL
      ssl: true
      # Whether the IMAP server uses StartTLS
      start_tls: false

      # The mailbox where incoming mail will end up. Usually "inbox".
      mailbox: "inbox"
      # The IDLE command timeout.
      idle_timeout: 60
    ```

1. Enable `mail_room` in the init script at `/etc/default/gitlab`:

    ```sh
    sudo mkdir -p /etc/default
    echo 'mail_room_enabled=true' | sudo tee -a /etc/default/gitlab
    ```

1. Restart GitLab:

    ```sh
    sudo service gitlab restart
    ```

1. Verify that everything is configured correctly:

    ```sh
    sudo -u git -H bundle exec rake gitlab:incoming_email:check RAILS_ENV=production
    ```

1. Reply by email should now be working.

### Development

1. Go to the GitLab installation directory.

1. Find the `incoming_email` section in `config/gitlab.yml`, enable the feature and fill in the details for your specific IMAP server and email account:

    ```yaml
    # Configuration for Gmail / Google Apps, assumes mailbox gitlab-incoming@gmail.com
    incoming_email:
      enabled: true

      # The email address including the `%{key}` placeholder that will be replaced to reference the item being replied to.
      # The placeholder can be omitted but if present, it must appear in the "user" part of the address (before the `@`).
      address: "gitlab-incoming+%{key}@gmail.com"

      # Email account username
      # With third party providers, this is usually the full email address.
      # With self-hosted email servers, this is usually the user part of the email address.
      user: "gitlab-incoming@gmail.com"
      # Email account password
      password: "[REDACTED]"

      # IMAP server host
      host: "imap.gmail.com"
      # IMAP server port
      port: 993
      # Whether the IMAP server uses SSL
      ssl: true
      # Whether the IMAP server uses StartTLS
      start_tls: false

      # The mailbox where incoming mail will end up. Usually "inbox".
      mailbox: "inbox"
      # The IDLE command timeout.
      idle_timeout: 60
    ```

    As mentioned, the part after `+` is ignored, and this will end up in the mailbox for `gitlab-incoming@gmail.com`.

1. Uncomment the `mail_room` line in your `Procfile`:

    ```yaml
    mail_room: bundle exec mail_room -q -c config/mail_room.yml
    ```

1. Restart GitLab:

    ```sh
    bundle exec foreman start
    ```

1. Verify that everything is configured correctly:

    ```sh
    bundle exec rake gitlab:incoming_email:check RAILS_ENV=development
    ```

1. Reply by email should now be working.