Bug: GUI gets threading wrong if mail happens to have same subject

[sebbASF]

Two e-mail threads with the same subject: 'mod_lua and subprocess_env' [1]

In the threaded and treeview modes, they are shown as part of the same thread (but they are not).

However if one clicks the individual Permalinks [2,3] the threading works properly.

[1] https://lists.apache.org/list.html?users@httpd.apache.org:2018-1:subprocess_env
[2] https://lists.apache.org/thread.html/31613d3c7a88a41ef9bf18df1a3c0e77d7eeda4b2d79f747ec9210b7@%3Cusers.httpd.apache.org%3E
[3] https://lists.apache.org/thread.html/c2a5654554abb620338190900ebc362b44d1336d9b15cecca73b395b@%3Cusers.httpd.apache.org%3E

[Humbedooh]

The subject finders need to be less aggressive, only try to find parent via subject if 'Re:, Fwd:, AW:' etc exists in the subject.

[sebbASF]

Surely the nesting needs to be driven by the Reference headers instead of the subject?

Looking for 'Re:, Fwd:, AW:' etc won't help if both original threads have responses.

[Humbedooh]

It is primarily driven by that yes - sometimes those headers are missing from replies, and we improvise to keep things sane. This isn't something new to Pony Mail, it's a de facto standard behaviour by most email clients (See https://www.jwz.org/doc/threading.html for some history)

[wrowe]

Is the converse also true? Noticed that the threaded browse is not forking off messages with changed subject lines, as they share a common thread-id. My other threaded views display the changed subject as a new thread, even if there is confusion about thread-id.

[sebbASF]

AFAIK, the subject line can change in a thread.
For example, JIRA messages include a [Created], [Updated] etc.
Unfortunately JIRA sends invalid References which don't match the Message-Ids exactly which makes threading tricky.

See also #439 which may be caused by incorrect matching on Subject:

[lhotari]

Bumping this issue.

We ran into this problem In Pulsar's dev mailing list recently and were wondering what was causing the behavior.
https://lists.apache.org/thread/jc7nbbpxr10g69wwkoz3h1yxyjd9ncpd