A New Outlook Rollout Scenario

Microsoft 365 Apps for enterprise customers should prepare to opt out of New Outlook starting in April 2027, The accompanying timeline (fig. 1) shows one of many possible scenarios for replacement of classic Outlook by new Outlook for Microsoft 365 E3 and E5 customers. In all scenarios, according to Microsoft, those customers will be able to deploy classic Outlook until at least 2029.

Microsoft plans to replace classic Outlook 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. 2027). New Outlook will be the default for both new and existing users, but organizations will be able to deploy classic Outlook side-by-side with Microsoft 365 Apps for enterprise.

Cutover. Microsoft will cut over Microsoft 365 Apps for enterprise users to new Outlook, and remove classic Outlook from Microsoft 365 Apps for enterprise.

In the scenario shown here, Microsoft provides 12 months’ notice of Cutover in the fourth quarter of 2028 and completes Cutover in the fourth quarter of 2029. That retires classic Outlook at the same time as Office 2024, which could be the last of Microsoft’s Long-Term Servicing Channel (LTSC) Office suites to include Outlook.