An email banner is a message that is added to the top or bottom of an email to provide some information or warning to the recipient. An email banner should be implemented to identify emails coming from external sources to prevent exposure of sensitive information and reduce the risk of corporate data being stored on non-corporate assets. An email banner can help employees recognize phishing or spoofing attempts and avoid clicking on malicious links or attachments. It can also remind employees not to share confidential information with external parties or forward corporate emails to personal accounts. The other options are not relevant or effective for this purpose. Reference: CompTIA Cybersecurity Analyst (CySA+) Certification Exam Objectives (CS0-002), page 13; https://www.csoonline.com/article/3235970/what-is-spoofing-definition-and-how-to-prevent-it.html