I'm having an intermittant problem with all the Windows machines on my
connecting to Courier IMAP. Error messages is:

Could not connect to server connection was refused

All machines are using Thundbird 2.04 as their IMAP client, machines
connecting from outside the LAN and my own machine which runs Linux do
have the problem.

Total number of similtaneous connections to the server I consider
fairly low,
typically between 30 - 60.

Machine is a Pentium D 3Ghz with 1GB RAM
CPU rarely hits double figures and generally stays below 5%
Mem usage is pretty low typically 600 -700 MB free with no swap space
Network Card is a Broadcom 10/100/1000 although looking at the output
dmesg there is a line:
tg3: eth0: Link is up at 100 Mbps, full duplex

which may be relevant.

Strange thing is if I restart Courier the problems go away for a

Any thoughts or suggestions greatfully received.

Kind regards,