MC1163753 – M365 Change Digest

One-line summary

Outlook on the web's activity-based timeout retires Jan 2026; admins should switch to Microsoft 365 idle session timeout for unified session management.

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Details

Summary

Outlook on the web's activity-based timeout (ABT) will retire by January 2026 (February for GCC/DoD). Admins must enable Microsoft 365 idle session timeout for consistent session control across apps. Users won't auto-sign out without it. Prepare by reviewing ABT use, enabling the new timeout, and updating documentation.

Body (from Message Center)

Outlook on the web activity-based timeout is retiring

To simplify session timeout management and improve consistency across Microsoft 365 apps, we’re retiring the activity-based authentication timeout (ABT) setting for Outlook on the web. Admins should transition to the Microsoft 365 idle session timeout, which provides a unified experience across supported Microsoft 365 web applications.

When this will happen:

The retirement will roll out in phases based on cloud environment:

Worldwide: Early January 2026 to late January 2026
GCC, GCCHigh, and DoD: Early February 2026 to late February 2026

How this affects your organization:

Who is affected: Users of Outlook on the web are affected by this change, as they will no longer be automatically signed out due to inactivity unless Microsoft 365 idle session timeout is enabled. Admins are responsible for configuring the replacement timeout setting.
What will happen:
- The ABT setting for Outlook on the web will be retired.
- If Microsoft 365 idle session timeout is not enabled, users will no longer be automatically signed out of Outlook on the web due to inactivity.
- Microsoft 365 idle session timeout applies across supported Microsoft 365 web apps.

What you can do to prepare:

Review your current use of activity-based authentication timeout (ABT) for Outlook on the web.
Enable Microsoft 365 idle session timeout to maintain session control across Microsoft 365 apps.
Communicate this change to your helpdesk and security teams.
Update internal documentation to reflect the new session timeout policy.
Review the previous retirement announcement: Activity-based authentication timeout for Outlook on the web.

Compliance considerations:

No compliance considerations identified, review as appropriate for your organization.

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      "Summary": "Outlook on the web\u0027s activity-based timeout (ABT) will retire by January 2026 (February for GCC/DoD). Admins must enable Microsoft 365 idle session timeout for consistent session control across apps. Users won\u0027t auto-sign out without it. Prepare by reviewing ABT use, enabling the new timeout, and updating documentation."
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