Resolution
goal
Top level Mailbox permissions are added to all sub-folders on the target mailbox.
cause
When a mailbox on the source server has granted permissions to another user at the top level (outlook today) they only have permissions to any subfolders they are explicitly granted access to. So if mailbox1 has given mailbox2 reviewer right at the top level and one sub folder called 'policies' then mailbox2 would have access to policies. If mailbox1 and mailbox2 are migrated with Exchange Migrator mailbox1's target mailbox will have mailbox2 listed as reviewer on all sub folders, not just policies anymore.
fix
This issue has been resolved in Exchange Migrator 2.2 service pack 1.
Top level Mailbox permissions are added to all sub-folders on the target mailbox.
cause
When a mailbox on the source server has granted permissions to another user at the top level (outlook today) they only have permissions to any subfolders they are explicitly granted access to. So if mailbox1 has given mailbox2 reviewer right at the top level and one sub folder called 'policies' then mailbox2 would have access to policies. If mailbox1 and mailbox2 are migrated with Exchange Migrator mailbox1's target mailbox will have mailbox2 listed as reviewer on all sub folders, not just policies anymore.
fix
This issue has been resolved in Exchange Migrator 2.2 service pack 1.
Additional Information
Formerly known as NETIQKB4684