Ever since I've been using debian and kde especially one thing has always bugged me, the date bars in kmail! These separate the mails into small chunks according to the day they were received, which sounds like a good idea until you see it implemented, and then you realise how inadequate it is because it closes the nested emails and breaks the threads. So I've been looking for a way to get rid of the date bars, and I've found one way.
In kmail go to
View -> Message List -> Aggregation and
tick Standard mailing list. The result is to get rid of the grey
bars completely and finally. Easy when you know how, its only taken me two months to find it out :)