After a migration to Microsoft Office 365, users cannot open a folder or add a hidden mailbox in Outlook. Also, users may receive the following error messages, depending on what they are trying to add or access.
- Additional mailbox
The name cannot be resolved. The name cannot be matched to a name in the address list.
- Additional Exchange account
The name cannot be matched to a name in the address list.
- Calendar or other folders
Microsoft Outlook does not recognize UserName.
This is expected behavior when you try to add a hidden mailbox.