Advice needed] SW for mail server

[Jai Rangi]

Greeting,
We are doing some restructuring for our mail server, Right now we are 
using Sendmail + Spam Assassin + courier-imap + horde. on one server and 
which is damm slow due to heavy traffic. Yes, We do have a lots of 
traffic, and processing more than 50K mails every day.
This new server will be basically a relay server, for incoming and 
outgoing mails. The existing will play the role of imap server.. .
There are so many mail programs available, We are looking for something 
better that
Sendmail + Spamassassin. on FC-4.
I will appreciate if you folks can share your Bench Marks and Logical 
thoughts...

Thank You,
-Jai

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