Should we use new Outlook or classic Outlook?

The short version

• New Outlook is the newer Windows app. Classic Outlook is the one with the File tab.
• Both work with Microsoft 365 mailboxes, shared mailboxes, POP and IMAP.
• Stay on classic if you depend on COM add-ins, big PST files or full offline work.
• Microsoft says classic Outlook is supported until at least 2029.
• You can switch back and forth while Microsoft is in its opt-in stage.

What’s the difference?

New Outlook for Windows is built on the same design as Outlook on the web. Classic Outlook is the long-standing desktop app with the ribbon and File menu. Our help page on setting up email in Outlook shows how to tell which one you have.

Microsoft keeps a feature comparison of the two. As of October 31, 2026, the gaps that matter most to small offices are:

Microsoft updates this table often. Check it before you decide, especially the rows marked “partly.”

How do I decide?

Ask three questions:

1. Does anyone use an add-in inside Outlook? Look under File, Options, Add-ins in classic Outlook. If a tool your business relies on is listed as a COM add-in, stay on classic for those people. Ask the add-in’s maker about a web add-in version.
2. Does anyone keep years of mail in PST files? New Outlook can import PST content, but doesn’t do everything classic does with them. Moving that mail into the Microsoft 365 mailbox or its archive is usually better than keeping PST files.
3. Does anyone work without internet for long periods? Offline support in new Outlook is still partial.

If the answer to all three is no, new Outlook is fine for that person. You can mix: one person on classic, the rest on new.

How do I switch, and switch back?

In classic Outlook, the Try the new Outlook toggle sits at the top right, according to Microsoft’s stages page. Turn it on to move to new Outlook. Microsoft says users can switch back to classic Outlook during this stage, and that the two apps can run side by side, so nobody is stuck. The exact switch-back control has moved between versions, so if you can’t see it, Microsoft’s “Run new Outlook and classic Outlook side by side” support page has the current steps.

When you first open new Outlook, it brings your accounts across. Check every account and shared mailbox appears before you rely on it. To add an account in new Outlook, select View, View settings, Accounts, then Your accounts.

What’s Microsoft’s timeline?

Microsoft describes three stages on its stages page, last updated February 23, 2026:

1. Opt-in (now). New Outlook is off by default. Users can try it with the toggle.
2. Opt-out. New Outlook becomes the default, but users can switch back. Microsoft says admins of managed enterprise plans get at least 12 months’ notice.
3. Cutover. Users can no longer switch back. Again, at least 12 months’ notice.

Microsoft also says existing classic Outlook installs “will continue to be supported until at least 2029.”

In March 2026, The Register reported that Microsoft moved the enterprise opt-out stage from April 2026 to March 2027. That came from a Microsoft 365 admin message, not the public Learn page, so treat it as reported rather than confirmed. Either way, nothing forces a small office to switch this year.

Why does it matter?

Outlook is where most of your customers’ messages arrive. A switch that silently drops an add-in, a shared mailbox or old archived mail causes real trouble on a busy day. Testing with one person first costs nothing.

What are the common mistakes?

• Everyone switching on the same day. Test with one person for a week.
• Deleting PST files after the switch. Move their contents into the mailbox first, and keep a backup.
• Treating the switch as permanent. It isn’t, while Microsoft is in opt-in.
• Blaming new Outlook for password prompts. Repeated prompts usually come from the account or a stale saved password. See why Outlook keeps asking for a password.

What if something is missing in new Outlook?

Switch back to classic Outlook and keep working. Note what was missing. Check Microsoft’s feature comparison again in a few months, since the table changes.

How much does it cost?

Nothing extra. Both apps come with Microsoft 365 plans that include the desktop apps, such as Business Standard and Premium. See which plan your team needs.

How does E-3 handle this?

Setting up Outlook is one of the most common email requests we get, with nearly 200 in our records for Outlook and Apple Mail alone. Before a move to Microsoft 365, we ask about mail kept only on one computer, such as PST files or POP accounts, so nothing is left behind.

Related questions

• How do I set up my email in Outlook or Apple Mail?
• Which DNS records change on moving day?
• Shared mailbox, distribution list or Microsoft 365 group?
• Back to the complete Microsoft 365 guide

Sources

1. Stages of migration to new Outlook for Windows (Microsoft Learn, updated February 23, 2026)
2. Feature comparison between new Outlook and classic Outlook (Microsoft Support)
3. Microsoft kicks new Outlook opt-out deadline down the road to 2027 (The Register, March 6, 2026)
4. Add an email account to Outlook (Microsoft Support)