SPF
SPF (Sender Policy Framework) is a DNS TXT record that lists which mail servers are authorized to send email claiming to be from a domain. A receiving mail server checks the SPF record of the domain in the message's envelope sender address against the IP that actually delivered the message; a mismatch can be treated as a sign of spoofing. SPF records use mechanisms like include:, ip4:, and mx to name authorized senders, and end with a qualifier (-all hard-fails unauthorized senders, ~all soft-fails) that sets how strictly a mismatch is treated. RFC 7208 defines SPF and caps lookups at 10 to limit DNS load.
By AdminKit team, Netbase JSC · Updated