Email Header
Email headers contain fields such as From, To, Subject, routing details, and authentication results. Learn which fields help investigate delivery and what to trust.
Email headers are fields before the message body, including From, To, Date, Subject, and Message-ID. Mail servers can add routing and authentication information as the message travels.
Visible fields and full headers
A mail client usually shows a small selection of fields. Its full-header or raw-message view exposes technical fields such as Received and Authentication-Results. In Gmail, use Show original to inspect them.
A decorative logo or banner at the top of an email’s body is a design header. It is separate from these message fields. The SMTP envelope used to route a message is also distinct from the From and To fields displayed to the recipient.
Read headers as evidence
Use the receiving provider’s trusted authentication results to investigate SPF, DKIM, and DMARC. Headers are not an independently verified record of every step: a sender can insert misleading fields, and authentication results should be trusted only when their source falls within the receiving system’s trust boundary. RFC 8601 describes that boundary.
Compare a failing message with a successful one. Look for a changed sending identity, authentication result, route, or delay, then match the Message-ID and timestamps to your provider’s logs. Full headers can contain addresses and internal host details. Remove those before sharing an example publicly.