Microsoft Purview | Share block at external users
Hello community. I have an issue with Microsoft Purview DLP policies. I am trying to create a policy that prevents documents from being shared through OneDrive with external users, while allowing certain exceptions. However, when I select the option "Block Access to external domains and users" and assign a specific email address to be blocked, it does not work. The configured email address is not being blocked. I was reviewing this with Copilot, and it mentioned that if the external user you are sharing with already exists in Entra ID, the tenant may treat the user differently (not necessarily as an external user). My external user exists in Entra ID as a Guest account. The external user is registered as follows: Displayname: User Name Userprincipalname: user.name_external.domain#EXT#@company.onmicrosoft.com User Type: Guest Has anyone else experienced this issue? I am sharing evidence of the policy configuration.Ask Microsoft Anything: Why Cybersecurity Needs a New Security Stack for the AI Era with David Weston
David Weston leads Agentic Security at Microsoft, where he and his team build the AI models, autonomous agents, and evaluation systems redefining how defenders operate. At Microsoft since the Windows 7 era, he has worked across exploit mitigation design, malware analysis, APT research, and led security engineering for Windows, Xbox, Azure OS, and Microsoft's Offensive Security Research & Engineering group. His current work is leading teams training frontier security models, agentic security systems for defenders, and pushing AI-driven vulnerability discovery through Microsoft's Multi-Model Agentic Scanning Harness (MDASH). A longtime member of the research community and former CISA technical advisor, David is a regular presenter at BlueHat, Black Hat, and DEF CON. Key areas Dave and his team can discuss: The vision behind Project Perception How AI is changing the economics of cyber offense and defense Lessons learned from building MDASH and Microsoft's AI security initiatives Security-first AI development and deployment What's next for defenders as agentic systems become mainstream This will be a TEXT-BASED AMA, so ask your questions in the comment section down below and David and team will be answering via comment replies during the live hour!
