Courier-imap consumes all available memory

[trinite]

I use a gentoo box as a web/mail/ftp/database server. It has about 100 mail users and hosts about 50 websites. Average load still is not higher then 0.02.
It uses qmail, courier-imap, spamassassin, clamav for mail sending/receiving and spam filtering. This all works fine, But there is one problem. After approximately two weeks running (after a reboot), the memory (1G memory, 1G swap) is growing with about 200 MB a day (the first two weeks, the swap stays almost empty, memory does fill up, but that seams normal, see Linux Memory Management or 'Why is there no free RAM?'). When memory and swap is filled up, it's even impossible to start a new ssh session to reboot the server. That has to be done by a reset.

Some weeks ago I was monitoring memory usage of the server and saw that courier-authlib was using a lot of memory, so I restarted the courier-authlib daemon, also triggering a restart of courier-pop3d, courier-imapd, courier-imapd-ssl. (courier-pop3d-ssl is not running). When I checked memory usage the server only uses 500 MB of memory. The next hours it grows to aproximately 1G. but swap was kept untouched for aproximately two weeks again.

After the two weeks the same happens again, and swap filled up with 200 MB a day. restarted courier-authlib again. Problem solved again...

It sure looks that courier-autlib is using a lot of memory if it runs longer than a few weeks. Is someone familiar with this problem (I can't find anyting about it in this forum, other forums or google). And does someone know a good solution for this problem? (I don't think restarting courier-authlib every two weeks is a good solution, although it keeps the server online )

Thanks in advance

[trinite]

Nobody?