findMeeting REST API does not support shared mailbox?

Hi Rashmi Ramakrishnan,

Welcome to Microsoft Q&A Forum!

Have a good day and I hope you're doing well!

I completely understand your concern. To confirm whether this was specific to your environment, I attempted to reproduce this scenario in my test tenant. I configured a Shared Mailbox with the necessary delegate permissions and called the findMeeting endpoint. 

I received the same "Unsupported Scenario" result as you did. 

Based on my research into the backend architecture, here is the likely reason for this behavior: 

The findMeetingTimes API is designed to be "context-aware." It calculates suggestions based on complex user data, such as personal preferences, working hours, and time zones. 

• User Mailbox: Possesses an interactive identity and a complete user profile context. 
• Shared Mailbox: In the backend (Azure AD/Exchange), a Shared Mailbox is technically a disabled user object without an interactive login session. 

When calling this API via delegation targeting a Shared Mailbox, the system likely cannot load the full "user context" required for the calculation algorithm to execute. It appears this specific API capability is restricted to fully licensed, interactive user accounts by design. 

Currently, I also could not find any official documentation explicitly listing Shared Mailboxes as an unsupported scenario for this endpoint.

However, the reproduction results suggest that this is the current behavior of the API for Shared Mailboxes, confirming that the issue is not with your implementation or code logic.

As a forum moderator, I am sharing this insight based on my own testing and research to help clarify the behavior. I hope this explanation saves you time from further troubleshooting. 

Best regards.

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The findMeeting API does not support shared mailboxes, which is why you are encountering the "Unsupported Scenario" error when trying to access the shared mailbox calendar. Currently, the Microsoft Graph API has limitations regarding the use of certain endpoints with shared mailboxes, and the findMeeting API is one of them.

For scenarios involving shared mailboxes, you may need to explore alternative approaches, such as using the getSchedule API, although you mentioned it does not work for your case. Unfortunately, there are no specific documents available that outline the functionality of the findMeeting API with shared mailboxes, as it is generally understood that this API is intended for individual user mailboxes only.

You may want to consider using the delegated permissions to access the shared mailbox directly, but keep in mind the limitations of the APIs available for shared mailboxes.