Authentication
What is Sender Policy Framework (SPF)?
An email authentication standard that lets a domain publish which mail servers are authorized to send on its behalf.
SPF is published as a DNS TXT record on the sending domain that lists the IP addresses and hostnames permitted to send mail for that domain. Receiving servers check the envelope sender (Return-Path) domain against this record and return a pass or fail. SPF authenticates the envelope sender, not the visible From address, and it breaks on forwarding because the relaying IP changes.
Why it matters for cold email
Cold email lands in spam without a valid SPF record because mailbox providers treat unauthenticated senders as suspicious. SPF must authorize every IP your sending tool or inbox provider uses, and you must stay under the 10 DNS-lookup limit or SPF returns a permerror and silently fails.
Related terms
Stop guessing at deliverability.
Scheduler Zero handles authentication, warmup, and sender reputation so your cold email lands in the inbox, not the spam folder.