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Glossary

Email Authentication

Also written: SPF DKIM DMARC, email sender authentication, domain authentication

Quick answer

What is email authentication?

Email authentication is a set of DNS records — SPF, DKIM and DMARC — that let receiving mailbox providers verify a message genuinely came from your domain and was not altered in transit. Without them, automated mail is far more likely to be filtered to spam or rejected outright.

Three records, all published in DNS, each answering a different question.

SPF — who is allowed to send

Sender Policy Framework lists the servers permitted to send mail for your domain. A receiving server checks the sending IP against that list.

The most common failure is the ten-lookup limit: chain enough include: statements and SPF evaluation fails, which is worse than having no record at all.

DKIM — was it altered

DomainKeys Identified Mail attaches a cryptographic signature to the message. The receiver verifies it against a public key in your DNS, which proves both origin and that the body was not modified in transit.

DMARC — what to do when a check fails

DMARC ties the other two together and publishes your policy: none (monitor only), quarantine (send to spam) or reject. It also enables reporting, which is the only way to discover who is sending as you.

Start at p=none, read the reports for a few weeks, then tighten. Publishing p=reject before you know every legitimate sender is how a company blocks its own invoices.

Why this is not optional any more

Google’s bulk sender requirements require SPF, DKIM and DMARC for senders above their volume threshold, along with one-click unsubscribe and a complaint rate kept under 0.3%. Yahoo published equivalent rules. Automated CRM mail sits squarely inside scope.

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