Email headers contain technical routing and authentication details like Received lines and Authentication-Results. Learn what headers include and how they’re used.
An email header is the technical metadata attached to every email message. Headers include details such as sender and recipient info, message IDs, the route the email took through servers (Received lines), and authentication outcomes.
Headers are critical for troubleshooting deliverability problems. They can reveal whether SPF, DKIM, and DMARC passed, which server relayed the message, and what IP address was involved in sending.
Because headers contain sensitive information, treat them carefully. When debugging, share headers only with trusted support channels and avoid posting them publicly. A header analyzer tool can summarize the key fields into a more readable format.