Microsoft Has Started Switching Off the Protocol That Apple Mail on Mac Still Depends On

On October 1, Microsoft began disabling Exchange Web Services, known as EWS, by default in Exchange Online. Apple's Mail and Calendar apps on the Mac still rely on EWS to sync Microsoft 365 work accounts, and the macOS update that would replace it has not arrived. The change is phased, so the first visible symptom will not appear for everyone on the same day.

What EWS is, and why Apple uses it

EWS is an interface that lets software other than Microsoft’s own clients read and write mail, calendars and contacts on an Exchange server. Microsoft introduced it with Exchange Server 2007, and for years it was the standard way for third-party apps, including Apple’s, to talk to Exchange. Microsoft’s current interface is the Graph API, which is the route Apple says its Mac apps must eventually take. The distinction matters because a Microsoft 365 account can still work in Outlook while the same account stops synchronising in Mail or Calendar.

A cutoff announced three years ago

The schedule was not a surprise. Microsoft stopped adding features to EWS in 2018 and said in 2023 that it would begin disabling the protocol in Exchange Online from October 2026. The October 1 step is the beginning of that plan, not the final shutdown. Microsoft describes a phased rollout, which explains why one tenant may continue working while another has already lost synchronisation. Administrators can temporarily switch EWS back on for their tenant, but only until April 1, 2027, when Microsoft plans to shut EWS down in Exchange Online permanently.

Where Apple stands

Apple’s Platform Deployment documentation says the company is “actively working with Microsoft” to move Mail, Calendar, Contacts, Notes and Reminders on Mac to the Graph API in a future macOS 27 update. Apple does not give a release date or identify a particular point release. MacRumors reports that macOS 27.1 was skipped and that the current macOS 27.2 beta notes do not mention Graph support. The practical conclusion is narrow: Apple acknowledges the migration, but users do not yet have a dated promise that native Mac apps will be ready before Microsoft’s final deadline.

Who is affected, and who is not

The change concerns Microsoft’s cloud-hosted Exchange service. Mac users who added a Microsoft 365 work account to Mail or Calendar are at risk, and only where their organisation has allowed EWS to be disabled. Companies running their own Exchange servers are not covered by this Exchange Online change. iPhone and iPad are also unaffected by this particular retirement because their built-in apps connect through Exchange ActiveSync rather than EWS. If work mail still arrives on an iPhone but has stopped on a Mac, a server-side protocol change becomes more likely than a local password problem.

What users and administrators should do

Individual users should ask their IT department before removing and re-adding the account. Reinstalling the account cannot restore a protocol that the server refuses. Outlook for Mac remains the obvious Microsoft-supported fallback, while the phone can cover urgent messages. Administrators should identify which tenants still depend on EWS, decide whether to keep it enabled temporarily, and test a Graph-capable client before April 2027. They should also watch Apple’s release notes for the first explicit mention of Graph support in the native Mac apps.

Why the asymmetry matters

The story is not simply that an old protocol is being retired. Microsoft has published a timetable for years; Apple has described the replacement without dating it. That leaves businesses managing two clocks: Microsoft’s hard April 2027 deadline and Apple’s undefined macOS release schedule. If Apple ships Graph support well before the deadline, the disruption will be a migration footnote. If it does not, organisations may move users to Outlook because it works, not because they prefer it. The immediate lesson is to treat a missing Mac sync as a compatibility warning, not as proof that the account or password is broken.

Bottom line

EWS is being retired in stages, and October 1 is the first operational warning. Microsoft 365 administrators have until April 1, 2027 to complete the transition in Exchange Online, while Apple has only promised a future macOS 27 update. Mac users should involve their administrator early and avoid assuming that deleting an account will fix a server-side retirement.