Outlook is not fully shutting down, but Microsoft is discontinuing the classic Outlook desktop application and replacing it with a rebuilt version simply called “new Outlook.” The classic app, long a staple of Windows and Microsoft 365, is being phased out as Microsoft shifts toward a unified, web-based architecture. This article answers the most common questions about what the change means, what is disappearing, and what it means for your email experience.
What is Microsoft actually replacing Outlook with?
Microsoft is replacing the classic Outlook desktop app with a new application also called Outlook, often referred to as “new Outlook.” The new Outlook is built on a web-based foundation, sharing its codebase with Outlook on the web (formerly Outlook Web App). It is not a third-party product or an entirely different email client, but a fundamentally rebuilt version of the same brand.
The shift means the new Outlook looks and behaves more like a browser-based application running natively on Windows. Microsoft has been gradually rolling it out across Windows 10 and Windows 11, and it is now the default mail client on new Windows 11 installations. The goal, according to Microsoft, is to deliver a consistent experience across devices and operating systems, including Mac, while reducing the overhead of maintaining separate codebases for desktop and web.
Which version of Outlook is being discontinued?
The version being discontinued is classic Outlook, the traditional desktop application that has been part of Microsoft Office and Microsoft 365 for decades. This includes the standalone Outlook application bundled with Office 2016, Office 2019, Office 2021, and the version included in Microsoft 365 subscriptions on Windows. It is the familiar application with the full ribbon interface, local PST file storage, and deep Windows integration that many users have relied on for years.
It is worth noting that Outlook for Mac is a separate product with its own development path, and classic Outlook for Mac is not subject to the same discontinuation timeline as its Windows counterpart. The version being phased out is specifically the Windows desktop classic Outlook application.
When is Microsoft ending support for classic Outlook?
Microsoft has confirmed that classic Outlook will reach end of support in 2026. Specifically, Microsoft 365-connected versions of classic Outlook on Windows are scheduled to lose support, meaning Microsoft will stop providing updates, security patches, and feature development for the classic app. After that point, the new Outlook becomes the supported path forward for Microsoft 365 subscribers.
For users on perpetual Office licenses such as Office 2021, support timelines follow the standard Microsoft lifecycle policy for that product version rather than the Microsoft 365 subscription schedule. However, the direction of travel is clear: Microsoft intends new Outlook to be the only actively supported Outlook experience for Windows users going forward, making 2026 a meaningful deadline for organizations still relying on the classic app.
Why is Microsoft moving away from the classic Outlook app?
Microsoft is moving away from classic Outlook primarily to reduce engineering complexity and accelerate feature delivery. The classic app was built on a legacy codebase that required significant separate development effort from the web and mobile versions. By converging on a single web-based architecture, Microsoft can ship new features to all platforms simultaneously rather than rebuilding them multiple times.
There are also strategic reasons tied to Microsoft’s broader cloud-first direction. The new Outlook integrates more tightly with Microsoft 365 services, including Teams, Loop, and Copilot AI features. Running on a web-based foundation makes it easier to embed cloud capabilities directly into the email client without the constraints of a traditional desktop application. From Microsoft’s perspective, the classic app had become a bottleneck to innovation rather than an enabler of it.
What features are missing from the new Outlook?
The new Outlook currently lacks several features that power users and organizations have depended on in classic Outlook. While Microsoft is actively closing the gap, as of 2026 some notable omissions and limitations remain:
- Local PST and OST file support is absent, meaning users cannot work with locally stored email archives in the same way.
- COM add-ins are not supported, which affects businesses relying on third-party plugins for CRM, compliance, or productivity tools.
- Offline functionality is more limited compared to the classic app, which was designed to work robustly without a constant internet connection.
- Advanced calendar and task features, including certain delegation and shared mailbox behaviors, have not been fully replicated.
Microsoft publishes a feature comparison document that is updated regularly as new Outlook matures. Organizations evaluating the switch should review that document against their specific workflows before committing to migration, particularly if they rely on add-ins or local data storage.
How does Outlook’s transition affect email deliverability?
The Outlook transition has real implications for email deliverability, particularly for email marketers and senders. The new Outlook renders emails differently from the classic app because it uses a different rendering engine. Classic Outlook on Windows used Microsoft Word’s rendering engine, which had well-documented quirks. The new Outlook uses a web-based rendering engine, which generally handles modern HTML and CSS more predictably.
For recipients, this means emails that were designed with classic Outlook’s rendering limitations in mind may display differently in new Outlook. Senders who have spent years coding around classic Outlook’s CSS limitations may find their templates need updating. More broadly, the transition also affects how Microsoft handles filtering and junk mail detection, as the new Outlook relies more heavily on Microsoft’s cloud-based filtering infrastructure, which processes sender reputation signals differently than local rules did in the classic app.
Monitoring how your emails perform across the shifting Outlook user base is important during this transition period, as rendering changes and updated filtering behavior can affect open rates, click rates, and inbox placement metrics.
How Email Industries helps with the Outlook transition
We understand that changes to major email clients like Outlook create real uncertainty for senders. Rendering shifts, updated filtering logic, and evolving authentication requirements can all affect whether your emails reach the inbox and look the way you intended. Our email deliverability services are designed to help organizations stay ahead of exactly these kinds of platform changes.
Here is how we help during transitions like this:
- Real-time inbox monitoring to detect changes in placement and rendering across Outlook and other major clients before they become bigger problems.
- Authentication setup and compliance management to ensure your SPF, DKIM, and DMARC records meet Microsoft’s evolving requirements.
- Proactive reputation management so that shifts in Microsoft’s cloud filtering infrastructure do not catch your sending domain off guard.
- Ongoing strategic guidance tailored to your sending environment, not one-time fixes that leave you exposed the next time something changes.
If the Outlook transition has raised questions about your deliverability setup or inbox performance, our Deliverability Assurance Packages offer continuous monitoring and expert support to keep your emails landing where they should. Feel free to contact us to talk through what your organization needs.
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