Debian 5 to CentOS 5 : nerver do such thing
i just want to tell everyone : nerver migrate a ZCS running on a Debian 5 server to a CentOS 5 one, even more if your CentOS runs on a KVM.
First of all you must know that CentOS 5.5 can hang randomly on a KVM, and nobody seems to be able to explain why (google on it). It just output some kernel panic messages, hangs up, and then run fine during 1 week, or 1 month, or more, then hangs again...
But the second thing you must know is that Debian 5 uses perl 5.10 and CentOS uses perl 5.8.
You'll need to compile perl 5.10 and all the packages needed by Zimbra via cpan on you CentOS. And beleive me, there is a lot of stuff.
Moreover, whatever you use as syslog subsystem (syslog, rsyslog, syslog-ng, ...), your stats and charts will be up during one day then stops. Can't figure out why. (not a killall/sudo problem)
Using CentOS 5 on KVM to run Zimbra, even more if you make a migration from a previous installation based on Debian 5, is a very very BAD choice.
You'll be warned.
Don't also try to migrate a 32 bits installation to a 64 bits one. It's just a mess.
To use Zimbra on your corp, you NEED to use a NE version, not an OSE.
Please, think to admins like me that come after the horrible choices you've made to save money...