SPF is an email authentication standard that lists which servers can send email for your domain. Learn how SPF works, the 10-lookup limit, and common mistakes.
SPF (Sender Policy Framework) is an email authentication method that helps receiving servers verify whether an email was sent from an authorized server for a domain. Domain owners publish an SPF record in DNS that lists permitted sending sources.
When a message arrives, the receiving server checks the SPF record and compares it against the sending server’s IP. If the sender isn’t authorized, SPF can fail, which increases the likelihood of spam placement or rejection, especially when combined with DMARC enforcement.
SPF has a well-known constraint: a maximum of 10 DNS lookups during evaluation. Too many includes or redirects can exceed this limit and cause SPF to fail. Keeping SPF simple and validating changes helps protect deliverability.