Cloud‑managed Remote Mailboxes: Manage Exchange attributes in Exchange Online (and finally retire the last Exchange server)
TL;DR: Microsoft shipped a new per‑mailbox capability that transfers the Source of Authority (SOA) for Exchange attributes to the cloud. Flip a switch (IsExchangeCloudManaged) and you can manage aliases, GAL visibility, custom/extension attributes, and many mailbox flags directly in Exchange Online for directory‑synced users, without keeping an on‑prem Exchange server (or EMT VM) just for recipient admin. Identity fields (name, title, UPN, etc.) remain mastered in on‑prem AD. Phase 2 adds write‑back of selected attributes …