Microsoft Teams Meetings – Join URL Validation

Microsoft Teams will validate meeting join URLs starting September 30, 2025, to prevent altered or rewritten links from blocking access, affecting users of the old Teams calendar app. The new calendar app redirects safely without blocking. No admin action is needed for Safe Links users; third-party URL rewriting must exclude Teams links.

Summary:

This may impact the meeting URLs received when rewritten or scanned by Time of Click protection.

Product and Environment

Spambrella – Proofpoint URL Defense Services (ALL)

Microsoft Notice

Outbound link to Admin Centre here.

Information

To ensure that Microsoft Teams join links function correctly when delivered via email, we recommend adding the teams.microsoft.com domain to the URL Defense allow list so that the domain will neither be rewritten nor scanned by click time protection.

Sign in to Spambrella/Proofpoint and navigate to Security Settings / Malicious Content / URL Defense, then add teams.microsoft.com to the ‘Exclude URLs that contain specified domains/IP addresses’ section. Contact support for further assistance or to discuss any concerns.

What and Who

To enhance the security and integrity of Microsoft Teams meetings, we are introducing a new feature that validates Teams meeting join URLs. This update helps ensure that meeting links are not altered or rewritten by security products in ways that could render them unusable or flagged as malicious. This is applicable only when users Join a meeting from Teams old calendar.

Rollout Schedule

• Worldwide: September 30, 2025
• GCC, GCC High, DoD: November 30, 2025

Impact on Your Organization

• Who is affected: Organizations that use security solutions to inspect or rewrite URLs, as well as users who join Microsoft Teams meetings through the Teams platform, will be affected by this update.

What will happen:

• Users using New Calendar App: For the new calendar app in Teams, Meeting joiners will not be blocked, instead, users will be redirected to Outlook Safelinks and again redirected to the destination. This feature is enabled by default and does not require admin configuration. For more information on New calendar in app in Teams follow this link: https://support.microsoft.com/en-us/office/get-started-with-the-new-calendar-in-microsoft-teams-98f3b637-5da2-43e2-91b3-f312ab3e4dc5

Old Teams Calendar App:

• Microsoft Teams will validate join URLs to ensure they have not been modified.
• If a join URL is rewritten or altered by a security product, it may be marked as malicious.
• Users will be prevented from joining meetings if URLs are not in their original format.
• This feature is enabled by default and does not require admin configuration.
• Microsoft’s advanced email security platform, including Safe Links (URL inspection/rewriting), will not be impacted by this update.
• Safe Links Behavior: Does not rewrite the URLs behind the “Join Teams meeting” or “Join” buttons. Only rewrites URLs within the meeting invitation body. Any temporary rewriting (if applied) is removed by Exchange Online upon send/receive.
• Outlook Add-in Behavior: If meeting links are rewritten via Outlook add-ins during meeting creation, there is no impact.
• Potential impact: This change may affect third-party security services that rewrite both the body URLs and the “Join” button URLs.

Platforms affected

• Only Microsoft Teams is affected, other platforms like Outlook web and win32, Outlook mac remain unaffected.