Microsoft Teams to let admins block external users via Defender portal

Microsoft announced a new integration between **Teams** and **Microsoft Defender for Office 365** that lets security admins centrally block external users and domains via the Tenant Allow/Block List, supporting up to 4,000 domains and 200 emails, contingent on enabling two Teams admin settings; rolling out early to mid-January 2026 for Defender Plan 1/2 customers, the update also introduces warnings for suspicious external traffic and default protections such as malicious URL detection, weaponizable file type protection, and false-positive reporting to help mitigate social engineering abuse by cybercrime and ransomware groups.