A private channel in Microsoft Teams is a new feature that allows confidential conversation and sharing to occur in a space that other users and even admins wont be able to see.
We came across a client that was unable to communicate out to people outside of the organization. A check of the Teams admin settings in the GUI showed that everything was configured properly
New ways to secure email use old tools like transport rules, some are anti-phishing rules, some are cloud app security policies, some are conditional access.