Definition
Email authentication header analysis involves inspecting the technical headers applied to an email as it passes through receiving servers. These headers — particularly Authentication-Results, DKIM-Signature, ARC-Seal, and SPF checks — reveal how the recipient's mail server evaluated the message's authenticity. Analysis helps diagnose why legitimate emails land in spam, confirms whether authentication is correctly configured, and identifies alignment issues between sending domains.
Key Headers
- Authentication-Results: Summary of SPF, DKIM, and DMARC evaluation by the receiving server
- DKIM-Signature: Cryptographic signature verifying email integrity during transit
- ARC-Seal: Authentication chain preserving results through email forwarding
- Received-SPF: SPF check result showing which IPs are authorised to send for your domain
- DMARC policy: Organisational DMARC policy applied and whether the email passed alignment checks
Best Practices
- Check authentication headers weekly on a sample of sent emails to detect configuration drift
- Use header analysis when troubleshooting deliverability drops for a specific ISP
- Compare authentication results across ISPs since different providers evaluate headers differently
- Forward raw email with full headers to deliverability tools for automated analysis
Related Glossary Terms
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.
DKIM (DomainKeys Identified Mail)
DKIM (DomainKeys Identified Mail) is an email authentication method that uses digital signatures to verify that an email was not tampered with during transit and comes from a authorised domain.
DMARC Alignment
DMARC identifier alignment determines whether the domain in the From header matches the domains used in SPF and DKIM authentication. Strict or relaxed.
DMARC (Domain-based Message Authentication)
DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication protocol that builds on SPF and DKIM to prevent domain spoofing and provide reporting on authentication failures.
Acceptance Rate
Acceptance rate is the percentage of emails submitted for delivery that are accepted by the recipient's mail server, representing the first deliverability checkpoint before inbox placement is determined.