(continued) By the way, my KMail version is 1.9.1 using KDE 3.5.2. The cache deleting advice by Eythian is great and solves the problem (at least, this time). You have to delete the files at: .kde/share/apps/kmail/imap Including the hidden ones beginning by "." -- kmail crashes on startup https://launchpad.net/bugs/48034