I have Azure DirSync setup, working.  Have been syncing user groups for Office, OneDrive, SharePoint.  No Exchange online.  Exchange is completely on prem.

No issues with syncing users, licensing for Office, OneDrive all good.

Now I need to start syncing some groups for SharePoint permissions.  I've added OUs for groups to partitions that will sync with DirSync.  Some groups sync okay, others cannot be seen in Azure.  It appears that the groups that are not syncing are all distribution groups.  Again - no - Exchange Online, Exchange is on Prem.

What is required to sync an on prem distribution group in Azure?

There are a few reasons why this could happen. Could be they are all missing an attribute that causes them to not be synchronized.

Start with IDFix to see if it finds any problems with AD.

Then open up the FIM Sync Service Manager

• 64-bit: %SystemDrive%\Program Files\Microsoft Online Directory Sync\SYNCBUS\Synchronization Service\UIShell/MIISClient.exe
• Then in the Management Agents tool, right click the MA and select Search Connector Space, In the drop down search by rdn. Type in CN=My Distrib group name and search. Then double click the object and use the Preview button to see what happens. This should show you where in the sync process it is stopping this object. Then you can adjust the data in AD so it works.