[Courier-imap] Courier Cannot display the list of messages

[Bikov M. <m....@ho...>]

Sorry my bad English
I have established qmail-ldap, and courier-imap v 3.0.6
on Xeon 2.8 RAM 4000Gb, Maildir on IBM FAStT 600 StourageServer
I have the following problems, At quantity of connections> 100
my Courier Cannot display the list of messages in folders (With random 
ip) and to load messages
Other clients at this time work normally - The problem is solved only 
"restart Courier-Imap?
The condition of connection - is established

in conf imap
MAXDAEMONS=1800
MAXPERIP=25

What can be the reason in refusal of service?

Thanks for answers