With Message Recipients Count requirement and Block Message action or Move All Recipients to BCC field action those situations will never happen. This requirement will count recipients per message, user, domain or any other condition based on message properties. See all conditions and exceptions.
|Limit the number of TO, CC and BCC recipients|
Good policy is to block the message and inform sender about the reason why it was blocked. Block Message action have option to customize the message which is delivered to sender.
|Define custom reject message while connection.|
This action is simple. No options or configurations need to be done.
|Prevent recipient names from showing by using Bcc|
Learn more about policies which can be applied with MSH Traffic Policy to your mail server.