When source or target domains schema is extended, for example to 2003 R2 or 2008 R2, new attributes are introduced. Are they migrated as well?
The behavior is by design.
QMM has static pre-defined attribute mappings and does not read it from AD dynamically. There are a number of attribute list templates at the moment of writing this article (as of QMM 8.5 release):
Windows 2003 R2
Windows 2008 R2
When you create new domain pair QMM console checks AD and Exchange version for source and target directories and generates corresponding attribute mapping for that pair.
If source or target directory schema is upgraded in the middle of migration, QMM mappings are not updated automatically and old schema mappings are still utilized. Thats why it is not recommended to perform any schema updates in the middle of migration project. This can also lead to the problem where DSA is no longer functioning properly and domain pair needs to be deleted and recreated. More information can be found in this Quest KBSOL36255:
Synchronization is broken after schema on the source domain was upgraded to 2003.
New attributes from Windows 2003 R2 are included in QMM as of version 8.2. 2008 R2 schema is supported as of QMM version 8.5. If particular schema version or extension to AD schema is not supported, please see this Quest KB article SOL25291 on what alternatives exist to bringing these attributes over:
Will Quest Migration Manager for AD (QMM) migrate non-default AD attributes in the environments where schema was customized?