Threaded email notifications by adding missing mail headers

[mxmehl]

Description

Currently, the email notifications lack some headers which would make them easier to read and follow in mail clients. Even in a modern MUA the notification mails aren't shown in a thread like with Github mails.

This is because following headers are missing (from a mail of a Github pull request):

• Message-ID: <astroidmail/astroid/pull/412/push/2025975904@github.com>
• In-Reply-To: <astroidmail/astroid/pull/412@github.com>
• References: <astroidmail/astroid/pull/412@github.com>

While the message-id isn't required to allow the threaded view it's part of a valid email layout.

[mxmehl]

Other interesting issues along the lines of improved email notifications:

#745, #2386, #2141, #1885, #1883, #1464, #145

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[ptman]

can message IDs be anything or do they need to confirm to a specific format?

[mxmehl]

can message IDs be anything or do they need to confirm to a specific format?

Basically this is quite free to define accoridng to RFC 2392 as long as every ID is globally unique. But in order to enable the tree structure, it should follow a certain form.

Github seems to do it as follows:

• First message: Message-ID: <$UserOrOrg/$reponame/$type/$number@$domain>, so e.g. astroidmail/astroid/pull/570@github.com
• Following replies:
  • Message-ID: <astroidmail/astroid/pull/570/issue_event/2191656010@github.com>, where the number is the comment ID
  • In-Reply-To: <astroidmail/astroid/pull/570@github.com>, so the Message-ID of the first post
  • References: <astroidmail/astroid/pull/570@github.com>, so the Message-ID of the first post

As you can see, no need to create new random strings, as the Gitea domain, the user/repo name, the pull/issue number, and the comment ID will make every Message-ID unique.

The missing Message-ID also causes Gitea's mails to be caught by more and more spam filters.

[mxmehl]

Closed by #7484 as it seems. Thanks @mrsdizzie !