Why Exchange Online Mailboxes have SharePoint Online Proxy Addresses

A post by the Exchange development group tried to explain why mailboxes have SharePoint Online proxy addresses. It’s all down to the Microsoft 365 substrate, which needs the proxy addresses to ingest digital twins from SharePoint Online into Exchange Online for use by shared services like Microsoft Search. The upshot is that you can’t remove a mailbox permanently without some background processes kicking in to make sure that SharePoint is taken care of.