Prepare to Opt Out of New Outlook Starting in April 2026

As managing vice president, Rob Helm covers Microsoft collaboration and content management. His 25-plus years of experience analyzing Microsoft’s technology... more

Microsoft 365 enterprise customers have a slightly firmer date when the “classic” Outlook for Windows app will be ejected from their Office suites and replaced with “new Outlook.” On Dec. 6, Microsoft announced it will start the Opt-Out phase of new Outlook’s rollout in Apr. 2026. By then, customers who buy Office through Microsoft 365 (formally known as Microsoft 365 Apps for enterprise) should be ready to either accept new Outlook and the possible breakage it brings, or block it in favor of classic Outlook, until the mandatory Cutover to new Outlook.

Directions on Microsoft’s diagram, embedded in this blog post, shows one way things could play out. If Microsoft runs Opt-Out for 18 months starting in Apr. 2026, the “Cutover” phase starts in early 2028. In this scenario, Microsoft will remove classic Outlook from Microsoft 365 Apps for enterprise by the second quarter of 2028, but it still will be available as a separate download for Microsoft 365 Apps for enterprise customers until 2029.

Directions on Microsoft members can find our advice and more details in our (frequently updated) full report M365 Customers Can Keep Classic Outlook Until at Least 2029. If you have Microsoft 365 Message Center read privileges, you can find Microsoft’s announcement of the Opt-Out phase in MC949965, Toggle to new Outlook.