courier imap

/etc/init.d/courier-authdaemon restart
/etc/init.d/courier restart

http://www.hard2get.org/apple/mail/apple-mail-plesk-imap.html
http://www.sfr-fresh.com/unix/misc/courier-imap-4.6.0.tar.gz:a/courier-imap-4.6.0/tcpd/couriertcpd.html
http://blog.makeitcomplete.com/2008/11/increase-the-number-of-connection-for-courier-imap-in-plesk/