Note:
According to an announcement in the Microsoft 365 Admin Center from February 2026, the start of the critical opt-out phase for business customers has been postponed from April 2026 to March 2027, so there is no immediate need to take action.

Am I affected?

Microsoft is gradually rolling out the new Outlook.

As of January 6, 2025, “Outlook new” is enabled by default for Microsoft 365 Business plans. However, the mandatory switch for businesses has been postponed and is now expected at a later date.

This change is mandated by Microsoft and primarily affects customers with Microsoft 365 Business plans.

• This change is mandated by Microsoft and primarily affects customers with Microsoft 365 Business plans.
• A timeline for Microsoft 365 Enterprise plans has not yet been published by Microsoft.
• Customers with Microsoft LTSC versions are not affected. According to current information, these versions will remain unchanged.
• If you use our Managed Service, we will take care of everything necessary for you.

What does this mean for me?

The new Outlook no longer supports some important features—this includes COM interfaces that many vendors use for specialized applications. This is also relevant for using key features in connection with our stp.one programs—for example, saving documents/emails in Documents via the Outlook add-in.

That’s why we recommend preventing the automatic switch to avoid disruptions to your workflows.

How can you prevent automatic migration?

stp.one recommends that administrators control the installation and use of the new Outlook by following the Admin-Controlled Migration Policy for the new Outlook for Windows.

This specifically includes disabling the migration policy. This prevents the automatic Outlook migration that Microsoft is pushing. If you use our Managed Service, we will disable this migration policy for you.

What can users do if they already switched to the new Outlook before migration was blocked?

Users can switch back from the new Outlook to classic Outlook, even if the toggle button is no longer visible. To do this, follow the steps recommended by Microsoft.

Are there any other impacts of the new Outlook on me?

Yes, there are a few open questions:

• POP3 and IMAP: Both protocols appear to be available in the new Outlook. However, it’s unclear if all features are fully supported. For IMAP accounts, login credentials may be transmitted to Microsoft servers, which could be relevant for data privacy.
• On-premises Exchange servers: Currently, on-premises Exchange servers are not officially supported. Microsoft is still investigating the situation.

Microsoft provides more information and a feature comparison here: New and classic feature comparison for Outlook for Windows.

For these reasons as well, stp.one recommends preventing the Microsoft-driven migration!

What other steps is stp.one planning to ensure compatibility with Office products?

• stp.one has released the Office LTSC (Long Term Support Channel) 2024 version.
  This on-premises version will be supported by Microsoft until at least 2029 and is generally not affected by the new Outlook migration. This gives you, in addition to switching to Microsoft 365, another option to use stp.one products independently of the Outlook migration.
• stp.one is planning/working on new Office.js-based add-ins to ensure compatibility with the new Outlook.

How will migration to the new Outlook work in the future?

You can find more information about the general Outlook migration process in the official documentation: Progressive phases of migration to a new Outlook for Windows.

Since Microsoft is pushing for a long-term switch to Microsoft 365, it’s a good idea to migrate to Microsoft 365 early. stp.one will also focus on the Microsoft 365 platform for future activities and developments.

Summary

By following the steps above, you can prevent the Microsoft-driven switch to the new Outlook. This ensures continued use of stp.one products for Outlook. stp.one is already working on compatibility with the new Outlook.