Narkyia is an email administrator and her email server is being used to send forged emails. What technology can she install to mitigate this issue?

Domain 4: Communication and Network Security Practice Questions
Questions from the following topics are included in this domain:   
Assess secure network design principles.   
Implement secure network design principles.  
Secure network components using network access control devices.   
Implement secure design communication channels.  
Understand data communications and virtualized networks.