Inga, I don't think that kind of lucky charm will work. In fact, Kmail works fine right after I log in. The problem begins about half an hour to one hour later.
Besides, I already have Kalarm running at startup. That should be enough. What do you think?
Oh, I just had the problem again. So this time I ran Kate and Konqueror as soon as I logged in. Then I ran Kmail. 15 minutes later... boom! Here comes the Kmail bug again. Cripes... :-(