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---
stage: Plan
group: Certify
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---
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# Reply by email
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> [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/1173) in GitLab 8.0.
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GitLab can be set up to allow users to comment on issues and merge requests by
replying to notification emails.
## Requirement
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Make sure [incoming email ](incoming_email.md ) is set up.
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## 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 ).
