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# Working with email in development

## Ensuring compatibility with mailer Sidekiq jobs

A Sidekiq job is enqueued whenever `deliver_later` is called on an `ActionMailer`.
If a mailer argument needs to be added or removed, it is important to ensure
both backward and forward compatibility. Adhere to the Sidekiq steps for
[changing the arguments for a worker](sidekiq/compatibility_across_updates.md#changing-the-arguments-for-a-worker).

In the following example from [`NotificationService`](https://gitlab.com/gitlab-org/gitlab/-/blob/33ccb22e4fc271dbaac94b003a7a1a2915a13441/app/services/notification_service.rb#L74)
adding or removing an argument in this mailer's definition may cause problems
during deployment before all Rails and Sidekiq nodes have the updated code.

```ruby
mailer.unknown_sign_in_email(user, ip, time).deliver_later
```

## Sent emails

To view rendered emails "sent" in your development instance, visit
[`/rails/letter_opener`](http://localhost:3000/rails/letter_opener).

[S/MIME signed](../administration/smime_signing_email.md) emails
[cannot be currently previewed](https://github.com/fgrehm/letter_opener_web/issues/96) with
`letter_opener`.

## Mailer previews

Rails provides a way to preview our mailer templates in HTML and plaintext using
sample data.

The previews live in [`app/mailers/previews`](https://gitlab.com/gitlab-org/gitlab-foss/tree/master/app/mailers/previews) and can be viewed at
[`/rails/mailers`](http://localhost:3000/rails/mailers).

See the [Rails guides](https://guides.rubyonrails.org/action_mailer_basics.html#previewing-emails) for more information.

## Incoming email

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:

   Configuration for Gmail / Google Apps, assumes mailbox `gitlab-incoming@gmail.com`:

   ```yaml
   incoming_email:
     enabled: true

     # The email address including the %{key} placeholder that will be replaced to reference the
     # item being replied to. This %{key} should be included in its entirety within the email
     # address and not replaced by another value.
     # For example: emailadress+%{key}@gmail.com.
     # The placeholder must appear in the "user" part of the address (before the `@`). It can be omitted but some features,
     # including Service Desk, may not work properly.
     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

     # Whether to expunge (permanently remove) messages from the mailbox when they are deleted after delivery
     expunge_deleted: false
   ```

   As mentioned, the part after `+` is ignored, and this message is sent to the mailbox for `gitlab-incoming@gmail.com`.

1. Read the [MailRoom Gem updates](#mailroom-gem-updates) section for more details before you proceed to make sure you have the right version of MailRoom installed. In summary, you need to update the `gitlab-mail_room` version in the `Gemfile` to the latest `gitlab-mail_room` temporarily and run `bundle install`. **Do not commit** this change as it's a temporary workaround.

1. Run this command in the GitLab root directory to launch `mail_room`:

   ```shell
   bundle exec mail_room -q -c config/mail_room.yml
   ```

1. Verify that everything is configured correctly:

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

1. Reply by email should now be working.

## Email namespace

As of GitLab 11.7, we support a new format for email handler addresses. This was done to
support catch-all mailboxes.

If you need to implement a feature which requires a new email handler, follow these rules
for the format of the email key:

- Actions are always at the end, separated by `-`. For example `-issue` or `-merge-request`
- If your feature is related to a project, the key begins with the project identifiers (project path slug
  and project ID), separated by `-`. For example, `gitlab-org-gitlab-foss-20`
- Additional information, such as an author's token, can be added between the project identifiers and
  the action, separated by `-`. For example, `gitlab-org-gitlab-foss-20-Author_Token12345678-issue`
- You register your handlers in `lib/gitlab/email/handler.rb`

Examples of valid email keys:

- `gitlab-org-gitlab-foss-20-Author_Token12345678-issue` (create a new issue)
- `gitlab-org-gitlab-foss-20-Author_Token12345678-merge-request` (create a new merge request)
- `1234567890abcdef1234567890abcdef-unsubscribe` (unsubscribe from a conversation)
- `1234567890abcdef1234567890abcdef` (reply to a conversation)

The action `-issue-` is used in GitLab as the handler for the Service Desk feature.

### Legacy format

Although we continue to support the older legacy format, no new features should use a legacy format.
These are the only valid legacy formats for an email handler:

- `path/to/project+namespace`
- `path/to/project+namespace+action`
- `namespace`
- `namespace+action`

In GitLab, the handler for the Service Desk feature is `path/to/project`.

### MailRoom Gem updates

We use [`gitlab-mail_room`](https://gitlab.com/gitlab-org/gitlab-mail_room), a
fork of [`MailRoom`](https://github.com/tpitale/mail_room/), to ensure
that we can make updates quickly to the gem if necessary. We try to upstream
changes as soon as possible and keep the two projects in sync.

Updating the `gitlab-mail_room` dependency in `Gemfile` is deprecated at
the moment in favor of updating the version in
[Omnibus](https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/master/config/software/mail_room.rb)
(see [example merge request](https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/5816))
and Helm Chart configuration (see [example merge request](https://gitlab.com/gitlab-org/build/CNG/-/merge_requests/854)).

#### Rationale

This was done because to avoid [thread deadlocks](https://github.com/ruby/net-imap/issues/14), `MailRoom` needs
an updated version of the `net-imap` gem. However, this [version of the net-imap cannot be installed by an unprivileged
user](https://github.com/ruby/net-imap/issues/14) due to [an error installing the digest
gem](https://github.com/ruby/digest/issues/14). [This bug in the Ruby interpreter](https://bugs.ruby-lang.org/issues/17761) was fixed in Ruby
3.0.2.

Updating the gem directly in the GitLab Rails `Gemfile` caused a [production incident](https://gitlab.com/gitlab-com/gl-infra/production/-/issues/4053)
since Kubernetes pods do not run as privileged users.

Note that Omnibus GitLab runs `/opt/gitlab/embedded/bin/mail_room`
instead of `bundle exec rake` to avoid loading the older version. With a
Kubernetes install, the MailRoom version has always been explicitly set
in the Helm Chart configuration rather than the `Gemfile`.

#### Preserving backwards compatibility

Removing the `Gemfile` would break incoming e-mail processing for source
installs. For now, source installs are advised to upgrade manually to
the version specified in Omnibus and run `bin/mail_room` directly as
done with Omnibus.

We can reconsider this deprecation once we upgrade to Ruby 3.0.

---

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