We've had Zimbra NE running for over a year now. We're very happy with it. Initially we did not enable anti-virus or anti-spam as we had a third party product.
We recently decided to turn on anti-spam only and ran into a serious problem. The amavisd daemon 100% flatlined the cpu on the mta's. It caused serious email delivery delays and thousands of messages in the deferred queue.
Our two MTA's our ESXi VM's. They're MTA & Proxy only. They have 4GB ram and 4 vcpu's.
Zimbra support had us change the max_server value in amavisd.conf.in from 10 to 50, which helped a little, but CPU was still at ~80% consistently. Memory usage and disk i/o are minimal.
Our mta's process about 40,000-60,000 messages daily each. Looking at the daily mail reports, we're maybe maxing 3-4,000 hourly during peak time.
We were under the impression two mta's should be able to handle that load easily so we're wondering if there are some amavis tweaks that can be made.