Guides

How SPF, DMARC, DKIM and MX work, written from the RFCs, with links to the checks and the findings they relate to.

• DKIM explained: selectors, keys and rotation
  How DKIM signing and key records work under RFC 6376: selectors, the v, k, p and t tags, key sizes after RFC 8301, Ed25519, rotation and revocation.
• DMARC explained: policy, alignment and reports
  How DMARC works under RFC 7489: alignment with SPF and DKIM, the p, sp and pct tags, report addresses, and how to move from none to reject safely.
• MX records explained: priority and null MX
  How MX records route email under RFC 5321: preference values, fallback to the address record, null MX from RFC 7505, valid targets and common mistakes.
• SPF explained: lookups, includes and all
  How an SPF record works under RFC 7208: mechanisms, qualifiers, the ten-lookup and two-void-lookup limits, include versus redirect, and common mistakes.

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