Classic Outlook end of support: what is really ending, and when

Headlines about classic Outlook “dying” mix up three different things: Microsoft making the new Outlook the default, Microsoft removing classic Outlook, and Office versions reaching the end of their support. Here are the dates for each, as Microsoft has announced them (checked 3 November 2026).

The short answer

• Classic Outlook for Windows is supported until at least 2029. Microsoft has committed to keeping the published support timelines of existing classic Outlook versions until at least 2029, for Microsoft 365 subscriptions and one-time-purchase Office alike.
• No date has been set for removing it. Microsoft calls that step the cutover and has promised organizations at least 12 months’ notice before it.
• What does change: from March 2027 the new Outlook becomes the default for business customers (the opt-out phase, moved from April 2026). People can still switch back to classic Outlook, and admin policies that block the new Outlook keep working.

Office versions that have already lost support

Outlook that came with a one-time-purchase Office follows that Office version’s dates:

“End of support” means no more security updates or fixes. The program keeps opening, and your PST files keep working, but running it on a computer connected to the Internet becomes a growing risk.

What happens to your PST files

Nothing happens to the files. PST is a format Microsoft publishes, and it will stay readable long after any one version of Outlook. What changes is the app you open them with:

• The new Outlook can open, import and export PST files, but opening one still needs classic Outlook installed next to it and a Microsoft 365 subscription. The details are in PST files in the new Outlook.
• Without any Outlook, the PST Viewer opens them in a browser on any computer, and the MSG Viewer opens single saved emails.

What to do now

1. Find your PST files. Archives often sit in more than one place: where is my PST file lists them.
2. Check they open. Old archives can carry damage that only shows during an import. The free health check reads every message and tells you.
3. Bring the mail you need into your mailbox while classic Outlook is still at hand: import a PST into Outlook. Split very large files by year first (PST file too large).
4. Keep a copy of each archive somewhere safe. A PST can be read without Outlook, now and later.
5. Only have an OST? It cannot be opened by the new Outlook or imported anywhere. Turn it into a PST with OST to PST while you still can.

Frequently asked

Will classic Outlook stop working in 2026? No. Microsoft supports it until at least 2029 and has not set a date to remove it. Only Office 2021 and older one-time-purchase versions have reached the end of their support.

Can I keep using classic Outlook after March 2027? Yes. March 2027 is when the new Outlook becomes the default at work; you can switch back until Microsoft announces the cutover, with at least 12 months’ notice.

I use Outlook at home. Does this affect me? The dates above are for business accounts. At home, the new Outlook already replaced Mail and Calendar in Windows; classic Outlook remains part of Microsoft 365 Personal and Family and of Office 2024.

Will I lose my old emails? Not if they are in a PST you keep. Emails in an Exchange or Microsoft 365 mailbox stay in the mailbox; only the local OST copy disappears when you stop using classic Outlook.

Where do these dates come from? Microsoft’s guide to product availability for the new Outlook, its Office lifecycle announcements, and the March 2026 admin notice moving the opt-out phase to March 2027, as reported by Petri.