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.
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).
1. Find the `reply_by_email` section in `config/gitlab.yml`, enable the feature and enter the email address including a placeholder for the `reply_key`:
1. Find the `reply_by_email` section in `config/gitlab.yml`, enable the feature and enter the email address including a placeholder for the `reply_key`:
```yaml
reply_by_email:
enabled: true
address: "gitlab-replies+%{reply_key}@gmail.com"
```
As mentioned, the part after `+` is ignored, and this will end up in the mailbox for `gitlab-replies@gmail.com`.
2. Find `config/mail_room.yml.example` and copy it to `config/mail_room.yml`: