Definition
Every email carries hidden headers that record its entire journey: the sending server, authentication checks, spam scores, routing path, and final disposition. Header analysis reads these to diagnose why an email bounced, went to spam, or was blocked.
Key Headers to Examine
- Received: Shows every server the email passed through, from sender to recipient
- Authentication-Results: SPF, DKIM, and DMARC verdicts from the receiving server
- DKIM-Signature: The DKIM signature and verification status
- DMARC-Filter: DMARC policy enforcement result
- X-Spam-Status: Spam filter score and threshold
- ARC-Seal: Authenticated Received Chain for forwarded email validation
Common Tools
Google Admin Toolbox, MXToolbox, and mail-tester.com provide header analysis. Most ISPs also offer raw header access via "show original" or "view source" options in the email client.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
ARPU (Average Revenue Per User)
ARPU (Average Revenue Per User) is a metric that measures the average revenue generated per email subscriber over a specific period, used to evaluate list value and campaign effectiveness.
Attention Rate
Attention rate is the percentage of email opens that last longer than 5 seconds, distinguishing genuine reads from passive opens, preview-pane views, or Apple MPP auto-loads.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.