Virtual Machine had 3.6GB RAM (maximum for 2.x version of VMware ESX server) and dual processor. (First we used 2GB ram and 1 processor but the startup times were 8minutes, so we "upgraded" machine and the startup times went to 4 minutes).
The aim of this test was to check whether Zimbra is suitable for our needs or not. Our users are not using calendar (yet) and most of them use Outlook for POP3/IMAP, so these to interfaces should be fast if we want to use it. And yes, as somebody said, we will be having more than 10 concurrent users, so 10 sequential users (as in test) is something really small for our systems.
I still think that Zimbra has the best web user interface available out there, but I doubt that this is all what we are looking for. When one of the bare-metal machines will be available, I will make the test again, to check whether virtual machines was the one causing slow response times.
The thing for our setup is that we are in doubt to move to new mail-storage engine, which does not bring anything new except the webGUI. Currently our setup is almost identical to zimbra, except using mbox storage and our web mail client. The problem is also with backup of the mails, since the only usable backup in ZCS case is using snapshots and if RHEL says that snapshots in Linux are not stable enough, we cannot afford to risk all users mailboxes. Restoring large number of files from tapes is really slow operation, so only snapshots are useful (and yes, we are so poor that we cannot afford SAN :)
I will also test the new version 3.2 when it will be released to check, whether it will perform better or not :) But I really think it will.
jernejp - as Dan (dkarp) mentioned we have some plans to make our IMAP/POP perf better. One thing that would help is if you collected the exact IMAP and POP commands your sending in your test. You can turn on debug in Zimbra and we will log this information (which might be the easiest way to collect the data). It will be best if you can run this test/debug against the new release which should be out very shortly.