KMail seemingly freezes when trying to open a message or executing any command on the local email folders (maildir) such as moving or marking of messages. Sometimes the triggered action is executed with very long delay or when restarting akonadiserver.Furthermore, Akonadi and the attached MySQL server are busy (but not fully occupied). For me, the problem probably came up after switching from MySQL to MariaDB on Arch Linux or after an update from KDE 4.11.1 to 4.11.2.The special issue here is that there is no specific error message or warning in Akonadi or KMail related to the source of the problem. Moreover, neither re-initializing all Akonadi databases nor re-installing or even downgrading kdepim packages solves the problem.
KMail extremely slow/frozen when operating on local maildir folder
mysql;kde4;kmail