Can't access a hidden mailbox in Outlook after a migration to Office 365 hybrid environment
Original KB number: 4034273
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.
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 recognizeUserName.
This is expected behavior when you try to add a hidden mailbox.
Auto-mapping enables users who have Full Access permissions to access a hidden mailbox. If you migrate from an on-premises environment, refer to the following article for instructions to enable auto-mapping in a hybrid environment: