I want to migrate users from my current Zimbra server behind a firewall to a new Zimbra server outside our firewall. The first go round I went from exchange to Zimbra without a problem. Are there any tools to migrate between installs to make it easy?

Current Server:

OS: Ubuntu 6.10 - 32 bit
Zimbra: Version 5.0.19_GA_3083.UBUNTU6.NETWORK

New Server:

OS: Ubuntu 8.04.3 LTS - 32 bit
Zimbra: Version 5.0.19_GA_3083.UBUNTU8.NETWORK