I would suggest using Dovecot. I'm not an expert with IMAP but dovecot
just works for me so I've never looked elsewhere.
http://www.dovecot.org
You could also try:
Courier-IMAP
http://www.courier-mta.org/imap/
Cyrus-IMAP
http://asg.web.cmu.edu/cyrus/imapd/
UW-IMAP (University of Washington)
http://www.washington.edu/imap/
To install on RedHat and Fedora Core:
up2date dovecot* <enter>
Debian and Ubuntu:
apt-get install dovecot-imapd <enter>
BSD users may need to use the pkg_add facility with a downloaded copy of
the Dovecot binaries from the main Dovecot site.
Usually Dovecot will start with little or no modification.
On the rare occasions it doesn't start, it's usually because of an error
regarding SSL or IPv6.
Disabling SSL and IPv6 (which are not essential for testing purposes)
can be achieved by changing the following settings in:
/etc/dovecot.conf or /etc/dovecot/dovecot.conf
To disable SSL support use the following settings:
protocols = pop3 imap
ssl_disable = yes
If you encounter IPv6 problems (Internet Protocol Version 6), tell
Dovecot to listen on IPv4 only by changing:
imap_listen = [::]
pop3_listen = [::]
to
imap_listen = *
pop3_listen = *
If you have any more questions then mail me directly as this isnt
strictly relevant to the exim list.
Thanks
Jason Meers