Diagnose email authentication and alignment from a real message
A reproducible checklist for comparing SPF, DKIM and DMARC DNS records with the identities in an authorized received email, and for telling authentication from alignment.
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Email authentication
Guides to SPF, DKIM, DMARC, DNS records, and domain alignment, including what to inspect when a check fails and how to verify a change.
DKIM selector not found: diagnose and repair
When a DKIM check fails with 'selector not found', the receiving server could not resolve the public key. Walk through the common causes and the verification steps.
DMARC quarantine vs reject — what to pick at each ramp stage
How to choose between DMARC policies p=none, p=quarantine, and p=reject as you move a new domain from monitoring into enforcement. The trade-offs and the failure modes.
SPF too many DNS lookups: diagnose and fix the limit
The SPF 10-lookup limit is one of the most common authentication failures. What causes it, what the error looks like, and the practical fixes that don't break your existing email flow.