Email Header Analysis
Also known as: Email Headers, Message Headers, Raw Headers
Email headers are metadata fields at the top of every email message that record the routing path, authentication results, sender identity, and content type. Reading raw headers is the single fastest deliverability diagnostic available: SPF, DKIM, DMARC, originating IP, and every relay server are all visible in the header block.
Every email has a header block that most senders never look at. Opening the raw headers of a message in spam vs. one that reached inbox shows the cause in 30 seconds.
Key headers for deliverability
- Authentication-Results: receiver-side report on SPF, DKIM, DMARC pass/fail. The first place to look.
- Received: each relay server adds a Received line showing IP, hostname, timestamp. Reading bottom-up traces the path from sender to recipient.
- Return-Path: the bounce address. Mismatch with From domain often signals forwarded or relayed mail.
- Message-ID: unique identifier; useful for tracking through logs.
- DKIM-Signature: the signature itself, plus selector and signing domain.
- List-Unsubscribe / List-Unsubscribe-Post: one-click unsubscribe headers required by Google/Yahoo bulk-sender rules.
Common diagnostic patterns
- SPF=fail, DKIM=fail: sending platform misconfigured for the domain
- SPF=pass, DKIM=fail: body was modified in transit (mailing list footer common cause)
- SPF=pass, DKIM=pass, DMARC=fail: alignment issue between From domain and authenticated domain
- Multiple Received hops from low-reputation relays: spam-classified path
How to view raw headers
- Gmail: Open message → three-dot menu → Show original
- Outlook: Open message → File → Properties → Internet headers
- Apple Mail: View → Message → Raw Source
- Use MxToolbox's Email Header Analyzer for parsed output
Frequently asked questions
Can headers be forged?+
Most can be forged; authentication results from the receiving server cannot. The Authentication-Results header is the trustworthy field because it's added by the receiver, not the sender.
Should I share raw headers when troubleshooting?+
Yes, but redact subject lines, Message-IDs, and personal addresses if sharing publicly. The headers themselves contain useful diagnostic data without exposing private content.
Put this concept into practice
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Related glossary terms
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