The user sees the following in the Console: "Backup scan failed: REST API is not yet supported for this mailbox".
This error may present for several reasons:
- The mailbox is on a dedicated Exchange Server.
- The mailbox is not a valid M365 mailbox or no longer exist.
- The mailbox is an Outlook.com account that hasn't been enabled yet.
- The mailbox is not part of an M365 plan that includes Flow.
Ultimately, it means that the mailbox does not have a valid license, in which case we are unable to back it up.
See Microsoft's recommendations here.