Header / Email header

An email header is a structured block of metadata that precedes the body of an email and contains essential routing and authentication information. Headers are generated by each mail server the message passes through, creating a trail from sender to recipient. 

Common fields in an email header include: 

• From, To, Subject, and Date (user-visible metadata) 
• Return-Path / Envelope From 
• Message-ID 
• Received lines showing the server hops and timestamps 
• Authentication-Results showing SPF, DKIM, and DMARC checks 
• MIME-Version, content type, and encoding details 

Email headers are primarily used by: 

• Inbox providers, to assess authenticity and filter spam 
• Postmasters and senders, to debug delivery issues 
• Email security tools, to trace spoofing, phishing, or misconfiguration