Hi @Agarwal Khushbu EXT ,
Welcome to our forum!
Based on my research, i found a Salesforce article that introduces:
Only shared folders, which provide delegate access to an inbox or calendar, are supported. Outlook shared mailboxes aren’t supported in Microsoft add-ins.
So i'm afraid the the add-in are not available with shared mailbox in Outlook. More information:
Considerations for Outlook Shared Folders in Outlook Integration
(Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
Hope to help you!
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.