Version: 1.9.5 (using KDE 3.5.5, Kubuntu (edgy) 4:3.5.5-0ubuntu3) Compiler: Target: i486-linux-gnu OS: Linux (i686) release 2.6.17-10-generic It seem that kmail will only thread launchpad (and other bug trackers) if the messages are from the same author. My thought is that this would be easy, as there is a bug id number in the subject of every launchpad email. Note: kmail can thread mailing lists fine.
It seems it can't thread bugzilla messages if it has not the "New:" one. Using Perfect, by reference and subject threading.
Possible duplicate of bug 279115.
Thank you for taking the time to file a bug report. KMail2 was released in 2011, and the entire code base went through significant changes. We are currently in the process of porting to Qt5 and KF5. It is unlikely that these bugs are still valid in KMail2. We welcome you to try out KMail 2 with the KDE 4.14 release and give your feedback.