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Microsoft has a DLP solution for MS Teams that is available with the E5 Compliance package
The solution is a reactive solution. This means that when sensitive data is sent in a file or message, the communication reaches the destination user and is deleted after the fact
The communication can be deleted quite quickly but also can take considerable time depending on various factors. Files can take up to an hour to be deleted.
Sensitive data appears in Windows and Mobile notifications and is not deleted at all.
In order for MS DLP to inspect external traffic, both the source organization and the destination tenant have to be on Teams Only Mode and using Native Federation.
MS DLP policies will not be enforced when a user is invited as Guest into an external tenant
MS DLP policies will not be enforced when a user joins a meeting that is hosted externally
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