We should support shared mailboxes. Steps involved:

• Add SupportsSharedFolders (https://learn.microsoft.com/en-us/javascript/api/manifest/supportssharedfolders) to manifest
• Review permissions. We apparently need to request Mail.Read.Shared (+ Mail.Send.Shared), additionally. This should not be done unconditionally, and may need an extra option. (https://learn.microsoft.com/en-us/answers/questions/1406369/access-shared-mailbox-via-graph-api)
• Review whether we need a separate graph url for this
• Add code to detect and/or configure sender address