What mail server will be able to handle a large amount of email?

Question

Email

Colleagues!
I am looking for a mail server that can handle a large amount of mail.
Zimbra Community Edition software. Now we have a mail archive for 500Gb of letters, about 200-300 letters are outgoing and incoming per day. 30 users. Year of operation of the organization +100Gb. Keeping such a mail archive is a pain! Accessing it for the user is even more of a pain! Increasing server performance does not solve permanent problems with availability and speed.
Advise some paid or free decision under such volumes of mail. Transfer to Google Apps and other cloud services is not an option, will not miss the Sat.

Answer 1

The issue is your infrastructure.
If you have a domain (or forest) and a server for 1,000,000-1,500,000 rubles is not a question for you - then Exch is definitely!
If you don't have the money for new hardware, you can try GroupWise . Licenses there are "paper", there is a trial period. But the Zimbra -> GW migration can eat your brain. The performance of GW will easily outdo both Zimbra and Exch.

Answer 2

You have a rather small mail archive and mail flow. What is your bottleneck in the system? Are you using Zimbra or Web desktop clients? Are IMAP clients being used?
What is the low performance? Long search, slow interface?