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SPF

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Sender Policy Framework — DNS TXT record listing which hosts may send mail for a domain; limited to 10 DNS lookups.

Platform & Operations. Last reviewed July 2026.

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2serious gotchas

1regular gotcha

3tips

Definition

SPF (Sender Policy Framework) is a DNS TXT record on a domain (or MAIL FROM domain) that lists which IP addresses / includes are authorized to send mail for that domain. Receivers check the SMTP envelope sender (Return-Path) against SPF. Common mechanisms include ip4:, ip6:, include:, and a/mx.

When to use it

  • Every sending domain and custom MAIL FROM domain used with Amazon SES or any ESP
  • As one leg of DMARC (alongside DKIM) for bulk-sender compliance

When not to use it

  • Flattening dozens of vendor includes into a single static IP list you never update — breaks when vendors rotate
  • Relying on SPF alone for brand protection — DMARC + DKIM are required for modern bulk rules

Tips

  • Stay under the 10 DNS lookup limit (include, a, mx, redirect, and exists count)
  • Prefer SES custom MAIL FROM so SPF authenticates a domain you control and can align for DMARC
  • Use ~all (softfail) or -all (fail) intentionally; softfail is common during migration

Gotchas

Serious

  • Lookup limit exceeded → SPF PermError → DMARC alignment fails even if “you included everyone”
  • Publishing SPF on the organizational domain but sending with a Return-Path that never matches

Regular

  • Multiple SPF TXT records on the same name (invalid) instead of one merged record

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Pictures:James Murray in the Scriptorium (public domain); Card Division of the Library of Congress, 1900–1920 (public domain); Salle des catalogues, Bibliothèque Mazarine, Paris, Marie-Lan Nguyen (CC BY 2.0); Copyright card catalog drawer, Michael Holley Swtpc6800 (public domain); Type in sort case, Edinburgh City of Print (CC BY 2.0); Widener Library reading room, 1920 (public domain). Via Wikimedia Commons.