Microsoft is replacing classic Outlook, gradually, and now even more gradually if you can believe it. The long-running desktop Outlook app is being replaced with a newer client called Outlook for Windows, with the goal of unifying Outlook across Windows, web, and mobile.
However, that transition does not appear to be going as smoothly as Microsoft hoped. It was recently revealed that the opt-out phase of the migration has now been pushed back by at least another year.
Now you might be wondering what the opt-out phase actually is, or where the opt-in phase fits into all of this. Well, that is where the migration timeline comes in.
The Microsoft’s Outlook migration timeline
Microsoft began the transition to the new Outlook for Windows back in 2022 with a private preview for testers. A public version followed in 2023, allowing users to try the new client if they opted in, and, honestly, I did not realize it had already been that long.
By late 2024, the new Outlook for Windows reached General Availability. That effectively meant it was ready for broader commercial use, and by December 202,4 Microsoft retired the Windows Mail app and replaced it with the new Outlook.
In 2025, Microsoft began pushing the transition further by automatically moving personal Microsoft accounts and some businesses to the new app. That rollout continued throughout the year as Microsoft tried to accelerate adoption.
Now in 2026, Microsoft has extended the deadline for enterprise users to prepare for the next stage. The opt-out phase will now begin in March 2027 instead of the original April 2026 target.
Microsoft says adoption of the new Outlook is picking up pace, according to TheRegister, but pushing the opt-out phase back another year suggests plenty of organizations are still not ready to make the jump.
That is not too surprising either. Outlook sits at the center of many business workflows, and when tools like that change, even small differences can create issues for people unfamiliar with the new software.
With support for classic Outlook continuing until at least 2029, it looks like this transition is going to remain a slow and gradual one for quite some time yet.
🗨️ Do you like the new Outlook app for Windows?
Have you or your business made the transition to the new version of Microsoft Outlook for Windows yet or are you still holding off?
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