SPF (Sender Policy Framework) allows the owner of a domain to specify which mail servers they use to send mail from

that domain.


An organisation sending mail publishes an SPF (TXT) record in the Domain Name System (DNS). The record contains a list of IP addresses that are authorised to send mail on behalf of their domain name.


Receivers of mail 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 mail on behalf of this domain is not listed in the SPF record, the message fails SPF authentication.


An SPF-protected domain is less desirable to spammers and is therefore less likely to be blacklisted by spam filters, ensuring that legitimate mail from that domain is delivered.


Once you have compiled a list of IP addresses permitted to send mail on your behalf, you can use a tool such as the following to create your record:


https://www.spfwizard.net/ 


This record then needs to be published to your domain name's DNS servers.