Converting mailboxes already migrated to Exchange Online to Shared mailboxes

hatsikidee , thanks for checking this!

One of the reasons for further checking and writing this blog was precisely the same curiosity you had, more specifically that it allows you to run the cmdlet in Exchange Management Shell and we do see Azure AD recognizing the change from on premises, while Exchange Online is not getting the memo to actually do the change 🙂

What we found during that investigation was that the design limitation is with the cmdlet itself, since Set-RemoteMailbox -Type Shared doesn't trigger for Migrated mailboxes as it does for Provisioned ones. That isn't something that we could modify the behavior for at this time, so the documentation for the cmdlet was modified to include this bit "A migrated shared mailbox cannot be converted to a regular mailbox and a migrated regular mailbox cannot be converted to a shared mailbox." to raise awareness.