Migration or backup creation failed with the following error:
Error: domain "domain.package" Unable to dump IP addresses for mail service Error: Value cannot be null. Parameter name: value
An internal issue with id #PPPM-2372. The issue has been fixed in Plesk 12, MU #38.
Please install all Plesk microupdates.
If this did not help, contact Odin Technical Support to fix the issue.