Fall back on `In-Reply-To` header for reply by email when sub-addressing with the reply key is not available.

See the discussion starting at https://gitlab.com/gitlab-org/gitlab-ce/issues/1360#note_1970380.

We could add the key to References, and read it from In-Reply-To as a fallback. Good idea.

Note that we're planning to add a feature to create an issue by email at some point, which will only work with a project/user-specific key in the address.

We need to expand the docs on the different options (sub-addressing, catch-all box, In-Reply-To).

mentioned in issue #1360 (closed)

Milestone changed to 8.0

I'm not sure this is a priority for 8.0 @DouweM

But I'm not against it.

@sytses It's not a priority, but I want Reply by email to be useable by as many customers/users as possible from the start. Chances are I won't get to it because of CI/CE and London, but I have it under 8.0 so I don't forget.

@DouweM Awesome!

mentioned in issue #1360 (closed)

Added reply by email label

Milestone removed

mentioned in issue #3240 (closed)

I have an immediate use for this as well as we just (sadly) moved from Gmail to Office 365. Now we can't reply to issues :(

Thanks all for putting this in queue.

Title changed from **Fall back on In-Reply-To header for reply by email when sub-addressing with the reply key is not available. ** to Fall back on In-Reply-To header for reply by email when sub-addressing with the reply key is not available.

Milestone changed to 8.5

Milestone changed to 8.6

mentioned in merge request !3024 (closed)

Added ~164274 label

Reassigned to @rymai

mentioned in merge request !3305 (merged)

Milestone changed to 8.7

mentioned in commit 31e76baf

Status changed to closed by commit 31e76baf

mentioned in commit c9a7cc4b