You have a Microsoft 365 E5 subscription.

You create a new data loss prevention (DLP) policy named DLP1 that protects financial data from being shared by using Microsoft Teams messages. You apply DLP1 to the users in the finance department.

An incident is raised when a finance department user named User1 shares financial data in a Teams channel that includes external members.

When User1 uses Teams to send the same message in a 1:1 chat or a private channel, the message is blocked as expected.

You need to ensure that User1 is prevented from sharing financial data in Teams channels that include external members.

What should you do?