How to remove orphaned permissions

Hello Everyone, 

As always I assigned Full Access, Send on Behalf and or Send As on certain mailboxes.

However I noticed if the account is not removed from these permissions, and the account is moved into our child domain, it is orphaned.  When I remove the access permissions I either get an error or when I re-open the properties it is still listed.

For example, I have a mailbox named Registration@contoso.com and I assign user1@contoso.com to have Full Permissions.

Then later I move user1 from the contoso.com domain to the child.contoso.com domain using the move-adobject cmdlet.  However if the full access permissions are not removed from the mailbox first it is orphaned on the account.

Unfortunately I cannot move the account  back to the parent domain as I cannot disrupt the user1 account.

Steps taken have been:

Open Registration AD account Attribute Editor and remove the User1 account from the msExchDelegateListLink Attribute.  When I do this I see on the User1 Attribute Editor the  Registration AD account is removed from the msExchDelegateListBL Attribute.  However it is still listed in Full Permissions on the Exchange mailbox properties.

If I remove the account from the msExchDelegateListLink then go and look in the account properties via ADSI it looks correct.

Any ideas how remove these orphaned permissions?

Thanks!