Deliverability & the inbox
SPF (Sender Policy Framework)
Also known as: sender policy framework · email authentication
A DNS TXT record that declares which IPs are authorised to send mail on behalf of a domain: one of the three email-authentication signals (SPF, DKIM, DMARC) mailbox providers check on every message.
SPF (Sender Policy Framework) is a DNS-level authentication mechanism: a TXT record published at the domain root lists which IP addresses and sending services are authorised to send mail as the domain. When a message arrives, the receiving server checks the return-path domain's SPF record against the connecting IP. Match = SPF pass. SPF alone is weak: it only verifies the envelope sender, not the displayed From address. That's why mailbox providers now require SPF paired with DKIM and wrapped in DMARC alignment to get full inbox credit. Common SPF mistakes: too many include: lookups (SPF has a 10-lookup limit), forgotten third-party senders (billing, support tickets) failing silently, and "-all" (hard fail) set too aggressively for the actual sending reality.