Version:            (using KDE KDE 3.1.3)
Installed from:    Debian testing/unstable Packages

I miss a feature that sylpheed ships: the possibility to hide the message view window. It allows you to have an extended view of all the messages in the current folder. But that's not all.
I check my email through IMAP, and an important part of it is usually spam. What I do is to select spam manually and delete it, but since kmail must always show the message before doing anything on it, I always have to end up displaying the spam messages before I am allowed to delete them, which is very annoying and time consuming.
On syplheed, the procedure is: tap a key to hide the message view window, then select the message without having to download or see its body and then delete it.
I think such a behaviour is a must-have in kmail. At least I find it very practical  :)