Every email carries a hidden record of its journey from sender to recipient. Learning to read headers turns a mysterious delivery failure into a diagnosable problem.
How to View Headers
- Gmail: Open email → three-dot menu → Show original
- Outlook: File → Properties → Internet headers
- Apple Mail: View → Message → All Headers
The Key Header Fields
Received (Multiple)
One "Received" header added by each server the email passed through. Read from bottom (first hop) to top (last hop). Timestamps on each show delivery time between servers — delays indicate where problems occurred.
Authentication Results
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of user@example.com)
dkim=pass header.d=example.com
dmarc=pass (p=reject)All three should show "pass." Any failure here explains deliverability problems.
X-Spam-Score / X-Spam-Status
SpamAssassin score added by many servers. Scores above 5.0 mean filtering; above 10 means rejection. Individual rules that triggered are listed.
Message-ID
Unique identifier for the message. Use this when contacting an ESP about a specific delivery failure.
Diagnosing Common Problems
- DKIM fail: Key not in DNS, or message modified in transit
- SPF fail: Sending server not in SPF record, or forwarding broke SPF
- Large time gap in Received chain: Greylisting or slow server
- High spam score: Review the specific rules that fired
Fix your authentication to pass all checks — then build reputation →