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When Will Microsoft Force New Outlook for Enterprise—and How Can IT Keep Classic Outlook Until March 2027?
What changed (and the new date)
Microsoft has extended the enterprise opt‑out timeline for the new Outlook for Windows: the opt‑out phase start moved from April 2026 to March 2027.
This is a 12‑month postponement that gives organizations more time to prepare, and it’s described as the second 12‑month extension of this deadline.
The update is referenced in Microsoft 365 Message Center item MC949965 (“Toggle to new Outlook”).
The timeline, in plain terms
Microsoft’s earlier plan was to auto‑move Microsoft 365 Enterprise users from classic Outlook for Windows to the new Outlook app starting in April 2026.
That forced timeline is now deferred, with the enterprise opt‑out phase beginning in March 2027 instead.
Microsoft frames the delay as a way to give companies more runway while it continues investing in feature work and incorporating customer feedback.
What this means for IT leaders
Treat the extension as schedule relief, not as a pause on planning, because the direction stays the same: Microsoft is still progressing toward the new Outlook experience.
Use the added year to reduce operational risk: identify critical workflows (shared mailboxes, add‑ins, compliance needs, delegation, archives), then confirm each one behaves as required in the new client before expanding rollout.
Plan for mixed-mode reality: some users will want to try the new app early, while others may need classic Outlook for specific tasks during transition.
A phased migration plan that usually works
- Define “ready” criteria per department: required features, add‑in compatibility, performance, and support readiness.
- Pilot first with a small group: include an executive assistant, a heavy calendar user, a shared mailbox owner, and a support agent (these profiles surface issues fast).
- Document fallbacks: keep a clear, supported path for users to temporarily switch back to classic Outlook during the rollout window.
- Communicate weekly: one short update on what’s changing, what’s not, and where users report issues.