Threading frequently fails with newer messages not placed under the original thread.
Here's how I perceive this problem:
Right click on Subject header in Message list and select Aggregation -> Configure
Select Standard Mailing List
Click Groups & Threading
Select Perfect or Perfect and by References
Now Message List is threaded correctly.
Wait for new messages to arrive.
Threading is now broken (sometimes).
Repeat steps above to restore correct threading.
I see this problem at work using an Exchange server proxied through an IMAP proxy (davmail) and at home using Gmail directly.
It's getting worse. Now there's no way that I see to restore proper threading. Later E-mail messages that are part of a prior thread are not sorted properly. This looks like it's permanent -- no way to get the message list window to sort threaded any more.
Thank you for reporting this bug in KDE software. As it has been a while since this issue was reported, can we please ask you to see if you can reproduce the issue with a recent software version?
If you can reproduce the issue, please change the status to "REPORTED" when replying. Thank you!