Systems and methods are described for providing customized message content to be displayed to a user of an email client, responsive to the user selecting, via a plug-in or agent of the email client, to report an email as a potential phishing email. In examples, the user may be an employee of an organization and the systems and methods may facilitate a determination by the plug-in or agent of the email client that the reported email is one that does not pose a security risk, such as a simulated phishing email sent by the organization itself, or an email sent from a trusted partner of the organization. The systems and methods may facilitate a customization of the message content that is displayed to the user. In examples, the customized message content may be included or specified within one or more SMTP extension headers of an SMTP email.