A New Outlook Rollout Scenario

Microsoft 365 Apps for enterprise customers should prepare to opt out of New Outlook starting in April 2026. The accompanying timeline (fig. 1) shows one Directions scenario for rollout of new Outlook and shutdown of classic Outlook in Microsoft 365 Apps for enterprise, the suite offered to Microsoft 365 E3 and E5 customers. The scenario is one of many possible: Microsoft has not announced when it will replace classic Outlook in Microsoft 365 Apps for enterprise. However, in all scenarios, Microsoft 365 Apps for enterprise customers will be able to deploy classic Outlook through at least 2029.

Microsoft is rolling out new Outlook for M365 Apps for enterprise in three phases.

Opt-In (now underway). Classic Outlook is the default, but users can switch to new Outlook in the application, unless their organization prevents it.

Opt-Out (begins Apr. 2026). New Outlook will be the default for both new and existing users, but administrators can intervene to keep classic Outlook and prevent switching. The Opt-Out phase will begin in Apr. 2026, according to a Microsoft 365 Message Center post (MC949965) first released in Dec. 2024.