working of mail server

Dear friends !!! Is suse E mail server II with post fix as MTA good enough to handle 700 Pop 3 users on a ML370 G2 Dual cpu PIII server with 760 MB of ram on a local lan network. suppose 1/4th of the users log in at a particular instance how does the email server take care that all of them have a fail proofconnection .I would like to understand the mechanism behind the working or handling of requests by an MTA. any suggestions would be a great help . what are the parameters that effect the performance of a mail server i have 128 Kb Bandwidth . Regards Raj