SPF. Sender Policy Framework
An SPF-protected domain is less attractive to fraudsters and is therefore less likely to be blacklisted by spam filters, ensuring that legitimate email from that domain is delivered.
SPF (Sender Policy Framework) allows the owner of a domain to specify which mail servers they use to send mail from that domain. A company sending email publishes an SPF record (TXT RR) in the Domain Name System (DNS). The record lists which IP addresses are authorized to send email on behalf of their domain.
Receivers of email verify the SPF record by looking up the “envelope from” (aka Mail From, Mfrom or return-path) domain name in the DNS. If the IP address sending email on behalf of this domain is not listed in the SPF record, the message fails SPF authentication.