Directory Synchronization is processing objects and synchronizing attributes, users are getting mail enabled but some or all of the groups are not getting mail enabled in target domain.
There are no errors and no visible issues, there is no explanation in the DSA.log file, source objects seem to be healthy and QMM is configured correctly.
This happens when a dedicated Expansion Server is being used in environment.
In this case groups have the homeMTA attribute populated, and QMM considers them to be a user object and therefore processes them incorrectly.
To work around this problem one can unset the Expansion Server back to Any server in organization, this will resolve the problem.
Note: a full resync might be needed in order to get target groups mail enabled.
Quest developers are aware of this issue and it will be resolved in QMM 8.5, an official Change Request 50632 exists.