ResolutionThe following actions should be performed:
1. Deassign Plesk Control Panel server from CMail without removing data (leave Remove all mail accounts from the mail server unchecked).
2. Migrate data from old CMail server to new CMail server using Plesk Backup Manager.
3. Assign Plesk Control Panel to new CMail server without mail content migration (checkbox Migrate mail must be left unchecked).
4. After assigning you should repair Plesk Control Panel assigned to new CMail server, this cause Plesk Expand will synchronize all records in the database.