Microsoft Teams will let admins block custom file extensions

Microsoft Teams will soon let administrators customize which file extensions are blocked in chats and channels, according to a new Microsoft 365 roadmap entry.

The change is an update to Weaponizable File Protection, a built-in Teams feature that scans conversations and blocks messages containing dangerous, high-risk file attachments commonly associated with malware and other security threats. Microsoft says administrators can either create their own blocked-file list or continue using the Microsoft-recommended default list.

The feature is currently in development and is scheduled to start rolling out in November 2026. When it reaches general availability, Microsoft says it will support Android, desktop, iOS, macOS, and web platforms in standard multi-tenant cloud environments worldwide.

Microsoft's support website currently says that administrators cannot change the list of blocked file types.

Starting in December, administrators will also be able to block external users through the Defender portal, according to Microsoft. The company has separately announced Teams protections that blur QR codes sent by external senders, let users report suspicious guest invitations, and automatically block identified external bots from joining meetings. These features are intended to address phishing, fraud, social engineering, and other attacks, but their availability may vary by rollout.