Version:           1.13.2 (using KDE 4.4.2)
Compiler:          gcc 4.4.3 
OS:                Linux
Installed from:    Debian testing/unstable Packages

After running for some time, or being told to load a few local folders with many messages, and many unread messages kmail will start to use up 350MB or more of ram quite easily. And closing folders that caused memory use to spike doesn't seem to free all the ram that was allocated to load the folder list. I can understand that loading a LOT of message headers might take a lot of ram, but it probably should be freed up later if its not going to speed up the process of loading the list at all (it doesn't seem to, loading a large folder with many unread messages still takes minutes no matter how many times you open and close the folder).

How to reproduce, load a large folder, see ram use increase by 100-200MBs easily.

Expected behavior, either use little ram, or put it to good use to make folders open instantly.

proof of memory use: 
moose    22312 48.9 14.0 1131460 565896 ?      Sl   22:44   8:54 /usr/bin/kmail -caption KMail