Problems with large folders in IMAP

Our server is using Dovecot to offer IMAPS mail storage.
The current version of Dovecot on SL4 (0.99) sometimes gives some problems with folders containing a large number of mails. In general it's better not going beyond 5~600 mails in frequently used mailboxes, like INBOX or Sent, and 2000 on less frequently used folders. We have not tried if using a different filesystem (eg ReiserFS instead of ext3fs) for mail storage may alleviate the problem.

In case of trouble with one or more folders, the first thing to try is to delete the index files which are build automatically by Dovecot. Before doing this, you must log out from mail: close your mail client, logout from webmail. Then login on the PSI server and

$ cd /MAIL/<username>/Maildir
$ find . -name ".imap.index*"
$ find . -name ".imap.index*" -exec rm {} \;

Make sure you type it exactly, and with the first find check that it only gets the right files - you might delete your own mail otherwise!