When migrating groups, some of them are not mail-enabled.
In some cases populated Exchange attribute homeMTA prevents the group from becoming mail-enabled. This is normally the case with the distribution groups having Exchange expansion server set.
The ADSI Edit snap-in can be used to look up and eventually clean this attribute for the source groups. If this solves the problemfor the few objectswhile multiple objects are affected, the ADCleanup or ADModify utilities can be used to clean up this attribute for multiple objects. Once this attribute is cleared the group will be processed by the Directory Synchronization Agent and mail-enabled.
Please also see this related solution:
Solution SOL9980 - How can I clean up the Service attributes used by DSA (Directory Synchronization Agent) during the matching process? -https://support.quest.com/SUPPORT/index?page=solution&id=SOL9980
The Migration Manager 7.x, 8.0, 8.1 Active Directory Cleanup Utility 1.1 utility can be downloaded from: