My current version:
OS: Ubuntu 8.04 LTS 32bit
Zimbra: 6.0.7 open source

Upgrade to:
OS: CentOS 6.4 64bit
Zimbra: 8.0.6 open source

Target:
New install the new version on another computer, have any methods to migrate all accounts from old to new?
I don't want add the accounts one-by-one. It almost 200 users.