Microsoft slows Outlook takeover as enterprise switch moves to 2027

Microsoft will make its web-based Outlook the default for managed enterprise accounts from March 2027, while extending Classic support until at least 2029 amid continuing gaps in offline use, add-ins and PST support.

Microsoft is still steering organisations towards the new Outlook, but it is doing so on a slower timetable than many users expected. The company now plans to make the new client the default for managed enterprise accounts from March 2027, while keeping the option to return to Outlook Classic for a period after the change. At the same time, Microsoft says classic Outlook will remain supported until at least 2029, which gives businesses more breathing room than the original migration schedule suggested.

That slower rollout reflects a product that is improving, but still not a complete replacement for the long-established desktop app. In a three-day test on Windows 11 Home 26H2, the new Outlook felt more usable than before, especially once its Classic-style theme was enabled through the appearance settings. Search was notably strong, with refiners and a dedicated files view that made attachments easier to find, while features such as snooze, undo send and scheduled send quickly became familiar. Microsoft has also reduced notification clutter by grouping new-mail alerts into a single summary.

The biggest advance is that offline use is no longer absent, but it remains limited. Microsoft now enables offline access by default in the new Outlook, with a rolling cache of mail from key folders and the option to extend the range to 90 or 180 days. That allows reading, searching, replying and queueing messages while disconnected, but important functions still fall short of Classic. Shared folders, the full address list, add-ins, calendar creation and some settings changes are not available offline, and Microsoft’s own comparison makes clear that Classic still has stronger offline handling.

Support for PST files is another step forward, yet it comes with conditions that undercut the convenience of the feature. Users can now open and work with PST archives in the new Outlook through the data files area, but Microsoft says Classic Outlook must also be installed, the app architecture must match, and Microsoft 365 is required. The feature is not available in the Arm version of the new Outlook, and Microsoft has indicated that broader PST support is still a work in progress, with bulk imports planned later.

For many organisations, the decisive issue is still add-in compatibility and application behaviour. The new Outlook supports web add-ins, but not COM add-ins or VBA macros, which means companies relying on older CRM, archiving or workflow tools may need redevelopment before they can move. Microsoft argues that COM add-ins can destabilise the client, but that explanation is cold comfort for IT teams with existing deployments. The app is also still noticeably less immediate than Outlook Classic, which remains a native Win32 programme, whereas Microsoft’s documentation describes the new client as a web-based experience running through WebView2.

That gap helps explain why Microsoft has softened its enterprise migration plan. Earlier this year, the company pushed back the opt-out stage by roughly a year, saying organisations needed more time to prepare. Home users and small businesses have already been moved onto the new client or given clear prompts to adopt it, but enterprise customers have a longer runway and can still keep using the classic desktop version for now. Microsoft’s latest stance suggests it is still filling in missing functionality before it tries to make the new Outlook the universal default.