Version: 1.12.90 (using 4.3.75 (KDE 4.3.74 (KDE 4.4 >= 20091102)), compiled sources) Compiler: gcc OS: Linux (i686) release 2.6.32-rc3-git1 When grouping messages by date messages with unknown date (eg. malformed) get grouped at literal timestamp 0, ie. January 1970. In message details "unknown" is shown correctly; such messages should be grouped as a separate group titled "Unknown". I don't think it makes any difference, but I noticed it on an IMAP connected GMail account.
Confirmed in KDE 4.4.0
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.