Just bumped into the following problem:

I have a Mailserver running with postfix (SMTP) and courier-imap (IMAP and IMAPS) - authentification is done with courier-authdaemon against a MySQL server. All of a sudden the IMAP-Server stopped working correctly - the connection was dropped but no error message was to be found in the logs. Even the usual subjects like problems with authdaemon seemed to work correctly according to the logs.

First thought was a client error - so I tried different clients from full featured like Thunderbird to Webbased (Squirrelmail) but no avail. Even a manual check via telnet either on the localhost or the external interface dropped the connection right after entering the login credentials.

Upon research I stumbled into this:
http://ubuntuforums.org/showthread.php?p=11902102#post11902102
The solution to replace gamin with FAM worked out and the server is up and running again. However old this thread in the ubuntu forum may be - according to my experience there is still an issue with gamnin.

During checking I also found a relation to the number of files in a directory (as I have a lot of incomming e-mail-traffic the file numbers may rise quite fast if I am away on holidays ...) I created a test account with only a few dummy e-mails copied directly into the Maildir and with this constellation everything still worked :-|

Sadly I forgot to check the file count once the error occured - but currently (about 8hs later) I ran a count on the file number in the Maildir that was affected - it returned 10215 Files - I can't see any "magic" number 2^x being crossed and my logs show less then 2000 Mails delivered to that account so 8192 does not seem a likely threshhold to be hit (also I am not really sure about this - and as it is a productive system I do not want to touch it, now it is up an running again).

If you need more information, just let me know.