What is one way to check if an attacker has tampered with the email header?

One effective way to check if an attacker has tampered with the email header is by examining the logs associated with email transactions. Email logs maintain a record of email communication, including sender and recipient details, timestamps, and routing information. By reviewing these logs, incident handlers can identify irregularities or discrepancies that suggest tampering, such as unexpected sender information, altered timestamps, or unusual routing paths.

Logs can also provide insights into whether messages were relayed or altered in transit, which is critical for understanding the integrity of the email's journey. These insights can help security teams determine if an attack has occurred and what kind of threat may be present.

While examining the email itself might provide some indication of tampering, it is the log analysis that provides a more comprehensive view and verification of the email's authenticity. For example, logs can show mail server activities that corroborate or contradict what is visible in the email header.