Knowledge base

Email authentication guides

Focused troubleshooting for the DNS records, alignment failures, and sender requirements that affect real email delivery.

GMAIL guide

Gmail 5.7.26 Fix

A practical checklist for fixing Gmail 5.7.26 authentication rejections and sender requirement issues.

SPF guide

Understand SPF ~all and -all policies and how to move a sender domain safely toward a stricter SPF posture.

DMARC guide

Learn how DMARC alignment works and how to confirm alignment with DNS and email headers.

DMARC guide

A beginner-friendly explanation of DMARC aggregate XML report fields and how to use them during policy migration.

GMAIL guide

Check the DNS side of bulk sender readiness before reviewing message-level and reputation requirements.

DMARC guide

Fix a DMARC record not found error by checking the DNS host, TXT value, propagation, and duplicate records.

SPF guide

Learn why multiple SPF records cause permerror and how to merge includes, IP addresses, and the final all mechanism.

SPF guide

Diagnose and fix the SPF ten-DNS-lookup limit without hiding unauthorized senders or breaking legitimate email.

DKIM guide

Find the correct DKIM selector and fix missing TXT or CNAME records for Google Workspace, Microsoft 365, and email platforms.

HDR guide

Fix DMARC failures when SPF passes for a return-path domain that does not align with the visible From address.

HDR guide

Understand why a valid DKIM signature can still fail DMARC and configure an aligned custom signing domain.

GEN guide

Choose a DMARC policy and move safely from monitoring to enforcement without blocking legitimate mail.

HDR guide

Read an Authentication-Results email header and identify SPF, DKIM, DMARC, alignment, and the trusted receiving server.

GMAIL guide

Troubleshoot Gmail 550-5.7.26 by testing SPF, DKIM, DMARC, alignment, PTR, TLS, and the actual sending stream.

GMAIL guide

Understand List-Unsubscribe, one-click POST handling, visible unsubscribe links, and what DNS tools cannot verify.