Microsoft extends the deadline for the classic Outlook app, weeks before the initial phase-out deadline.
The classic Outlook was expected to expire in April this year, but with this extension, Microsoft is giving users a grace period to transition smoothly to the new Outlook experience while it addresses users’ concerns.
The new Outlook is Microsoft’s planned replacement for the older version, designed to unify the email experience across platforms and closely align the web version with the performance and feature set of the classic desktop client. However, several limitations of the classic Outlook have caused many users to refuse the migration, prompting Microsoft to extend the phase-out deadline.
Details surrounding the delay
Outlook is Microsoft’s primary mail platform and an integral part of the Microsoft 365 ecosystem. Organizations that subscribe to Microsoft 365 use a mix of the Windows desktop app, the web version (Outlook Web Access, OWA), and mobile apps to send and receive email.
However, the primary reason for the support extension is the significant functional differences between the classic Windows desktop client and the new Outlook application. Because the new Outlook was essentially a desktop wrapper for OWA, it lacked several crucial features found in the classic app.
That difference created friction during the transition, forcing users who rely heavily on these capabilities to stick with their classic Outlook.
According to this Microsoft Learn report, key features that were either missing or deemed insufficient in the new Outlook for a complete corporate migration include:
- Lack of a complete offline mode: As a full desktop app, the classic Outlook can operate fully offline with cached mailboxes. The new one, being a webapp wrapper, requires a strong internet connection to work. As a result, users who travel frequently and may temporarily lose internet connectivity will often experience issues when using the new Outlook.
- PST problems: Organizations often rely on Personal Storage Table (PST) for mail data migration, external backups, and other data management needs. The new Outlook currently has limitations on how Outlook users can interact with PST files, another obstacle to a smooth transition.
- Issues with add-ons: The classic Outlook app supports several add-ons that integrate well with other Windows apps. Although the new Outlook comes with its own add-ons, it struggles with traditional Windows apps due to its web-first approach.
- Advanced customization and automation: Certain custom configurations and automation flows are lacking in the new Outlook. The new Outlook includes a simplified rules workflow, limiting the creation of complex rules and reducing UI customization, which power users favored.
Although Microsoft has begun addressing these issues, its implementation has been slow, and the transition phase gives it time to address all issues, while gradually onboarding users to the unified Outlook.
Delayed until at least April 2027
The current extension moves the classic client’s retirement date to at least April 2027, allowing users sufficient time to plan and migrate.
The revised date aligns with the start of Microsoft’s “Opt-out” phase (originally scheduled for April 2026), where the New Outlook will become the default experience. But users can still switch back to Classic Outlook if they wish.
However, according to another Microsoft Learn report on the three-stage rollout (opt-in, opt-out, and cutover), classic Outlook will still be supported for organizations and customers with perpetual licenses (such as Office LTSC) at least through 2029.
The prolonged support for enterprise users includes ongoing security updates and compatibility maintenance, giving companies a safer, extended runway for their migration plans. The exact “cutover” date for the classic client, when it will be fully retired for most users, has not yet been announced.
Also read: Microsoft is making other major timeline changes in 2026, with Windows 11, Office 2021, and several legacy products nearing end of support.
