Domain with disabled mail service cannot be migrated to PA, unless it is assigned to service template with mail resource type.
The following error is thrown when performing the migration:
error: Subscription is assigned to a service template '*Template_Name*' that has no 'mail service' Assign this subscription to a service template which offers Mail service
The behavior is caused by software issue #PPA-2086. The fix is included in MU #13.
Update PA to the latest version: