Can someone refer me to a simple webmail (script) using pop3/imap for about 50 users that can also support all the domains on my Raq3 server ?

Have you looked on http://www.hotscripts.com (there are a number of free scripts listed there - php and perl I believe).

there are some also over at http://www.thecgisite.com.

try looking under the perl, asp, or php sections.

or you can search :)