Migrating your users means you're going to have to deal with mail, calendar, contacts and passwords. This page used to be one monolithic monstrosity -- but has now been broken down into separate pages:
- Mail Migration
- Calendar and Contacts Migration
- Password Migration
- Email Rules Migration
- Zimbra to Zimbra Server Migration
Please see User Migration Troubleshooting if you are having problems migrating data to your Zimbra installation.