Version:           unspecified (using KDE 4.7.0) 
OS:                Linux

I've configured only one IMAP account with 200k+ emails from gmail. After some time kmail eats lots of my RAM (3G from 8G). Akonadi_imap_Resource eats additional 200M. Sometimes kmail eats my CPU (50-100% on Phenom x4 920 @ 3Ghz).
Here is the report from KDE syste activity:

Process 27542 - kmail

Summary

The process kmail (with pid 27542) is using approximately 3.1 GB of memory.
It is using 3.0 GB privately, and a further 20.5 MB that is, or could be, shared with other programs.
Dividing up the shared memory between all the processes sharing that memory we get a reduced shared memory usage of 7.7 MB. Adding that to the private usage, we get the above mentioned total memory footprint of 3.1 GB.
Library Usage

The memory usage of a process is found by adding up the memory usage of each of its libraries, plus the process's own heap, stack and any other mappings, plus the stack of its 2 threads. 
Private
more
3191704 KB	[heap]
1328 KB	/usr/lib/libQtWebKit.so.4.7.3
524 KB	/var/tmp/kdecache-me/icon-cache.kcache
280 KB	/usr/lib/libQtGui.so.4.7.3
220 KB	/usr/lib/libkdeui.so.5.7.0
Shared
more
14260 KB	/SYSV00000000 (deleted)
1640 KB	/usr/lib/libQtGui.so.4.7.3
880 KB	/usr/lib/libQtCore.so.4.7.3
756 KB	/var/tmp/kdecache-me/ksycoca4
392 KB	/lib/libc-2.14.so
Totals

Private	3197104 KB	(= 360 KB clean + 3196744 KB dirty)
Shared	20968 KB	(= 5744 KB clean + 15224 KB dirty)
Rss	3218072 KB	(= Private + Shared)
Pss	3205033 KB	(= Private + Shared/Number of Processes)
Swap	0 KB


Reproducible: Always

Steps to Reproduce:
1. Launch kmail :)
2. Wait for some time

Actual Results:  
Kmail eats my RAM!

Expected Results:  
I expected memory usage ~400M. Opera while browsing is eating 600M with the same email account configured with IMAP (and additional pop3).