Move reply by email docs to a new locationdocs/refactor-reply-by-email

[ci skip]

9 files changed, 635 insertions, 630 deletions

diff --git a/config/gitlab.yml.example b/config/gitlab.yml.example
index 1470a6e2550..b26c9f7ccc9 100644
--- a/config/gitlab.yml.example
+++ b/config/gitlab.yml.example
@@ -111,7 +111,7 @@ production: &base
 
   ## Reply by email
   # Allow users to comment on issues and merge requests by replying to notification emails.
-  # For documentation on how to set this up, see http://doc.gitlab.com/ce/incoming_email/README.html
+  # For documentation on how to set this up, see http://doc.gitlab.com/ce/administration/reply_by_email.html
   incoming_email:
     enabled: false
 
diff --git a/doc/README.md b/doc/README.md
index dd0eb97489e..cb378e68c60 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -42,7 +42,7 @@
 - [System hooks](system_hooks/system_hooks.md) Notifications when users, projects and keys are changed.
 - [Update](update/README.md) Update guides to upgrade your installation.
 - [Welcome message](customization/welcome_message.md) Add a custom welcome message to the sign-in page.
-- [Reply by email](incoming_email/README.md) Allow users to comment on issues and merge requests by replying to notification emails.
+- [Reply by email](administration/reply_by_email.md) Allow users to comment on issues and merge requests by replying to notification emails.
 - [Migrate GitLab CI to CE/EE](migrate_ci_to_ce/README.md) Follow this guide to migrate your existing GitLab CI data to GitLab CE/EE.
 - [Git LFS configuration](workflow/lfs/lfs_administration.md)
 - [Housekeeping](administration/housekeeping.md) Keep your Git repository tidy and fast.
diff --git a/doc/administration/reply_by_email.md b/doc/administration/reply_by_email.md
new file mode 100644
index 00000000000..5a9a1582877
--- /dev/null
+++ b/doc/administration/reply_by_email.md
@@ -0,0 +1,302 @@
+# 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.**
+
+[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).
+
+To set up a basic Postfix mail server with IMAP access on Ubuntu, follow
+[these instructions](./postfix.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"
+    ```
+
+    ```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"
+    ```
+
+1. Reconfigure GitLab and restart mailroom for the changes to take effect:
+
+    ```sh
+    sudo gitlab-ctl reconfigure
+    sudo gitlab-ctl restart mailroom
+    ```
+
+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"
+    ```
+
+    ```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"
+    ```
+
+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"
+    ```
+
+    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.
diff --git a/doc/administration/reply_by_email_postfix_setup.md b/doc/administration/reply_by_email_postfix_setup.md
new file mode 100644
index 00000000000..22f10489a6c
--- /dev/null
+++ b/doc/administration/reply_by_email_postfix_setup.md
@@ -0,0 +1,324 @@
+# Set up Postfix for Reply by email
+
+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 `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:
+
+    ```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 incoming email.
+
+    ```sh
+    sudo useradd -m -s /bin/bash incoming
+    ```
+
+1. Set a password for this user.
+
+    ```sh
+    sudo passwd incoming
+    ```
+
+    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, verify that `postfix` is running:
+
+    ```sh
+    sudo postfix status
+    ```
+
+    If it is not, start it:
+
+    ```sh
+    sudo postfix start
+    ```
+
+1. Send the new `incoming` user a dummy 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._
+
+    _**Note:** 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](#configure-postfix-to-receive-email-from-the-internet)._
+
+1. Check if the `incoming` user received the email:
+
+    ```sh
+    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:
+
+    ```sh
+    q
+    ```
+
+1. Log out of the `incoming` 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, requires mailboxes to have the Maildir format, rather than mbox.
+
+1. Configure Postfix to use Maildir-style mailboxes:
+
+    ```sh
+    sudo postconf -e "home_mailbox = Maildir/"
+    ```
+
+1. Restart Postfix:
+
+    ```sh
+    sudo /etc/init.d/postfix restart
+    ```
+
+1. Test the new setup:
+
+    1. Follow steps 1 and 2 of _[Test the out-of-the-box setup](#test-the-out-of-the-box-setup)_.
+    1. Check if the `incoming` user received the email:
+
+        ```sh
+        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:
+
+        ```sh
+        q
+        ```
+
+    _**Note:** 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._
+
+1. Log out of the `incoming` 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:
+
+    ```sh
+    sudo postconf -e "mydestination = gitlab.example.com, localhost.localdomain, localhost"
+    ```
+
+1. Let Postfix know about the IPs that it should consider part of the LAN:
+
+    We'll 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.
+
+    ```sh
+    sudo postconf -e "mynetworks = 127.0.0.0/8, 192.168.1.0/24"
+    ```
+
+1. Configure Postfix to receive mail on all interfaces, which includes the internet:
+
+    ```sh
+    sudo postconf -e "inet_interfaces = all"
+    ```
+
+1. Configure Postfix to use the `+` delimiter for sub-addressing:
+
+    ```sh
+    sudo postconf -e "recipient_delimiter = +"
+    ```
+
+1. Restart Postfix:
+
+    ```sh
+    sudo service postfix restart
+    ```
+
+## Test the final setup
+
+1. Test SMTP under the new setup:
+
+    1. Connect to the SMTP server:
+
+        ```sh
+        telnet gitlab.example.com 25
+        ```
+
+        You should see a prompt like this:
+
+        ```sh
+        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 setup to allow inbound traffic on port 25.
+
+    1. Send the `incoming` 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: incoming@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 `incoming` user received the email:
+
+        ```sh
+        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:
+
+        ```sh
+        q
+        ```
+
+    1. Log out of the `incoming` account and go back to being `root`:
+
+        ```sh
+        logout
+        ```
+
+1. Test IMAP under the new setup:
+
+    1. Connect to the IMAP server:
+
+        ```sh
+        telnet 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 `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.
+        ```
+
+    1. Disconnect from the IMAP server:
+
+        ```sh
+        a logout
+        ```
+
+## Done!
+
+If all the tests were successful, Postfix is all set up and ready to receive email! Continue with the [Reply by email](./README.md) guide to configure GitLab.
+
+---
+
+_This document was adapted from https://help.ubuntu.com/community/PostfixBasicSetupHowto, by contributors to the Ubuntu documentation wiki._
+
+[reply by email]: reply_by_email.md
diff --git a/doc/administration/restart_gitlab.md b/doc/administration/restart_gitlab.md
index 483060395dd..b561c2f82aa 100644
--- a/doc/administration/restart_gitlab.md
+++ b/doc/administration/restart_gitlab.md
@@ -139,7 +139,7 @@ If you are using other init systems, like systemd, you can check the
 
 [omnibus-dl]: https://about.gitlab.com/downloads/ "Download the Omnibus packages"
 [install]: ../install/installation.md "Documentation to install GitLab from source"
-[mailroom]: ../incoming_email/README.md "Used for replying by email in GitLab issues and merge requests"
+[mailroom]: reply_by_email.md "Used for replying by email in GitLab issues and merge requests"
 [chef]: https://www.chef.io/chef/ "Chef official website"
 [src-service]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/support/init.d/gitlab "GitLab init service file"
 [gl-recipes]: https://gitlab.com/gitlab-org/gitlab-recipes/tree/master/init "GitLab Recipes repository"
diff --git a/doc/incoming_email/README.md b/doc/incoming_email/README.md
index 5a9a1582877..db0f03f2c98 100644
--- a/doc/incoming_email/README.md
+++ b/doc/incoming_email/README.md
@@ -1,302 +1 @@
-# 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.**
-
-[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).
-
-To set up a basic Postfix mail server with IMAP access on Ubuntu, follow
-[these instructions](./postfix.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"
-    ```
-
-    ```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"
-    ```
-
-1. Reconfigure GitLab and restart mailroom for the changes to take effect:
-
-    ```sh
-    sudo gitlab-ctl reconfigure
-    sudo gitlab-ctl restart mailroom
-    ```
-
-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"
-    ```
-
-    ```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"
-    ```
-
-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"
-    ```
-
-    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.
+This document was moved to [administration/reply_by_email](../administration/reply_by_email.md).
diff --git a/doc/incoming_email/postfix.md b/doc/incoming_email/postfix.md
index 787d21f7f8f..90833238ac5 100644
--- a/doc/incoming_email/postfix.md
+++ b/doc/incoming_email/postfix.md
@@ -1,321 +1 @@
-# Set up Postfix for Reply by email
-
-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 `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:
-
-    ```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 incoming email.
-
-    ```sh
-    sudo useradd -m -s /bin/bash incoming
-    ```
-
-1. Set a password for this user.
-
-    ```sh
-    sudo passwd incoming
-    ```
-
-    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, verify that `postfix` is running:
-
-    ```sh
-    sudo postfix status
-    ```
-
-    If it is not, start it:
-
-    ```sh
-    sudo postfix start
-    ```
-
-1. Send the new `incoming` user a dummy 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._
-
-    _**Note:** 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](#configure-postfix-to-receive-email-from-the-internet)._
-
-1. Check if the `incoming` user received the email:
-    
-    ```sh
-    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:
-
-    ```sh
-    q
-    ```
-
-1. Log out of the `incoming` 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, requires mailboxes to have the Maildir format, rather than mbox.
-
-1. Configure Postfix to use Maildir-style mailboxes:
-    
-    ```sh
-    sudo postconf -e "home_mailbox = Maildir/"
-    ```
-
-1. Restart Postfix:
-    
-    ```sh
-    sudo /etc/init.d/postfix restart
-    ```
-
-1. Test the new setup:
-    
-    1. Follow steps 1 and 2 of _[Test the out-of-the-box setup](#test-the-out-of-the-box-setup)_.
-    1. Check if the `incoming` user received the email:
-    
-        ```sh
-        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:
-
-        ```sh
-        q
-        ```
-
-    _**Note:** 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._
-
-1. Log out of the `incoming` 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:
-    
-    ```sh
-    sudo postconf -e "mydestination = gitlab.example.com, localhost.localdomain, localhost"
-    ```
-
-1. Let Postfix know about the IPs that it should consider part of the LAN:
-    
-    We'll 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.
-    
-    ```sh
-    sudo postconf -e "mynetworks = 127.0.0.0/8, 192.168.1.0/24"
-    ```
-
-1. Configure Postfix to receive mail on all interfaces, which includes the internet:
-    
-    ```sh
-    sudo postconf -e "inet_interfaces = all"
-    ```
-
-1. Configure Postfix to use the `+` delimiter for sub-addressing:
-    
-    ```sh
-    sudo postconf -e "recipient_delimiter = +"
-    ```
-
-1. Restart Postfix:
-    
-    ```sh
-    sudo service postfix restart
-    ```
-
-## Test the final setup
-
-1. Test SMTP under the new setup:
-    
-    1. Connect to the SMTP server:
-        
-        ```sh
-        telnet gitlab.example.com 25
-        ```
-
-        You should see a prompt like this:
-
-        ```sh
-        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 setup to allow inbound traffic on port 25.
-
-    1. Send the `incoming` 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: incoming@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 `incoming` user received the email:
-    
-        ```sh
-        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:
-
-        ```sh
-        q
-        ```
-
-    1. Log out of the `incoming` account and go back to being `root`:
-
-        ```sh
-        logout
-        ```
-
-1. Test IMAP under the new setup:
-    
-    1. Connect to the IMAP server:
-        
-        ```sh
-        telnet 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 `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.
-        ```
-
-    1. Disconnect from the IMAP server:
-
-        ```sh
-        a logout
-        ```
-
-## Done!
-
-If all the tests were successful, Postfix is all set up and ready to receive email! Continue with the [Reply by email](./README.md) guide to configure GitLab.
-
----------
-
-_This document was adapted from https://help.ubuntu.com/community/PostfixBasicSetupHowto, by contributors to the Ubuntu documentation wiki._
+This document was moved to [administration/reply_by_email_postfix_setup](../administration/reply_by_email_postfix_setup.md).
diff --git a/doc/install/installation.md b/doc/install/installation.md
index 3ac813aa914..da3f92f9a6c 100644
--- a/doc/install/installation.md
+++ b/doc/install/installation.md
@@ -563,7 +563,7 @@ Using a self-signed certificate is discouraged but if you must use it follow the
 
 ### Enable Reply by email
 
-See the ["Reply by email" documentation](../incoming_email/README.md) for more information on how to set this up.
+See the ["Reply by email" documentation](../administration/reply_by_email.md) for more information on how to set this up.
 
 ### LDAP Authentication
 
diff --git a/lib/tasks/gitlab/check.rake b/lib/tasks/gitlab/check.rake
index 5f4a6bbfa35..2ae48a970ce 100644
--- a/lib/tasks/gitlab/check.rake
+++ b/lib/tasks/gitlab/check.rake
@@ -671,7 +671,7 @@ namespace :gitlab do
           "Enable mail_room in the init.d configuration."
         )
         for_more_information(
-          "doc/incoming_email/README.md"
+          "doc/administration/reply_by_email.md"
         )
         fix_and_rerun
       end
@@ -690,7 +690,7 @@ namespace :gitlab do
           "Enable mail_room in your Procfile."
         )
         for_more_information(
-          "doc/incoming_email/README.md"
+          "doc/administration/reply_by_email.md"
         )
         fix_and_rerun
       end
@@ -747,7 +747,7 @@ namespace :gitlab do
           "Check that the information in config/gitlab.yml is correct"
         )
         for_more_information(
-          "doc/incoming_email/README.md"
+          "doc/administration/reply_by_email.md"
         )
         fix_and_rerun
       end