When User A shares the inbox through Outlook delegate option to User B, we cannot add that inbox as secondary mailbox. Every time we should use the “View Other User’s Folder” and select the name from GAL to view that inbox.
This is because the other user provides permission only to the Inbox. So when we add the mailbox in the advanced option, the Outlook Contacts exchange server and checks the ACL values listed in the Top of the information Store. Since the user has provided access only to the Inbox, there won’t be any Permission value and hence it errors out.
The solution for this issue is to provide access to the Root of the Mailbox. That is Top if the Information Store. This can be done in two ways.
1. Provide Access to the Root
2. Through Powershell (Only be Exchange Admins).
Provide Access to the Root.
User A who has delegated his Inbox to User B and User wanted to add the Inbox permanently to the Outlook. Now User A should right click on his email address(Root) and goto Data File properties, Click on Permission, Click on Add and select User B and give appropriate permission. This will add the permission entry to ACL, but the user B can view only the folders that has been given access.
Through Exchange Powershell.
Now the user B has been given with delegated permission to User A’ inbox, Exchange Admins can run this command in the Exchange Powershell.