Recommend a webmail system?

Hello

I have a couple of POP servers running sendmail/qpop - one running debian
sarge and the other slackware. These are primary and secondary servers with
common users. Users poll both servers from their desktop mail clients.

I currently provide web-based access to each server through the usermin
module that bolts into webmin. Users have to remember to check both servers
independantly. Usermin does the job but is fairly clunky and I would like
to install a webmail system with a better UI. For security, I would love the
install the webmail system on a web server [recent PHP and Apache] and use
it to poll user accounts on the two mail servers.

I have already considered and dismissed the following:

a) atmail [http://atmail.com/webmail_client.php], no multiple mail accounts
b) Openwebmail [.org], little more functional
than Usermin but, again, does not allow polling of more than one account.
c) mailbee [http://www.afterlogic.com/mailbee/] - PHP version is limited
and, again, no multiple accounts.

Can anyone here recommend anything - preferably from experience?.

Many thanks

Lee