I have been put in charge of researching possible E-mail servers for my company, not knowing much about unix, can anyone give me some url's or names of unix based e-mail servers so I can research features?

<P>Current email architectures follow an n-tier construct where the presentation logic is decoupled from the application logic and the datastores. This means that your system (if the company is big) should have datastores where email is stored/archived that are completely independent of the mail routing and filtering application logic.<P>
The mail routing and filtering application logic should be decoupled from the user mail client. This means that you could use any kind of client, from a web browser, Outlook, POP/IMAP clients, wireless phones, etc. to access mail.<P>
The application logic helps you route mail in a complex orgainzation, filter mail, etc. This may be tied to a directory service (i.e LDAP) or other directory system.
<P> Take a look at http://www.n-tier.com to understand n-tier architecture and then apply the idea to your mail analysis. If you do this, you will be moving your organization into the future, not taking them backwards into older 2-tier client server models (and certainly not back to older monolithic/vertical email applications).