Both application and delegated permissions are supported.
If you use delegated permissions, you can add Mail.Read.Shared or Mail.ReadWrite.Shared, and use auth code flow to get the token.
If you use application permissions, you can add Mail.Read, and you can use the client credentials flow to get a token.
More details can be found at the link:
https://learn.microsoft.com/en-us/graph/outlook-share-messages-folders#microsoft-graph-permissions
Hope this helps.
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