This week I had an Office 365 migration, with a very strage case:

I migrated all of the users to Office 365 with AADConnect, and when creating a new outlook profile, directly some additional mailboxes were added.

There were NO mailbox rights set yet !

I’ve checked the mailbox rights with powershell, en there were no active settings.

I’ve created a ticket @Microsoft and tested several things.

Solution 1:

Go to the attribute editor of the affected User, en select the attribute : msExchDelegateListLink

Delete all the available users, en delete them from the list => Click OK 2 times and sync again with AADCOnnect

Solution 2

Go to the server where AADConnect is installed, and start the “Synchronization Rules Editor” => Select “In from AD – User Exchange” => Edit

Select No

Go to Transformations => go to msExchDelegateListLink => Change the Flowtype to Expression => change the source to “NULL”=> click Save.

Solution 3

Completely reinstall The AADConnect, and deselect the attribute msExchDelegateListLink