@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
This guide helps you with the choices you could face when selecting the right hardware.
Existing Zarafa customers should also definitely download the pdf. Because the guide also provides you with tricks to tweak your server set-up.
Get a copy of the guide by leaving your details. You will receive a link aftwards which will help you to access the presentations again at any time.