The DNS SPF record is used in mail domain reputation. The Sender Policy Framework (SPF) allows a domain owner to specify in a DNS record the list of servers which can be trusted for sending email for the domain. The main objective is to reduce the amount of SPAM and phishing sent from a domain on behalf of the official servers.
The content of the SPF information is stored in a DNS TXT record with a prefix v=spf1 associated with a domain record. Multiple information can be provided and a useful include function is available for automatically inserting the SPF information from a provider.
Each mail server receiving an email from a server (eg MTA – mail transfer agent) can check whether the origin can be trusted and take a routing or delivering decision accordingly. By requesting the DNS SPF record associated to the sender domain, it can obtain the list of servers that are authorized to send email, either their IP address (field ip4 or ip6), their name (field a) or their mail exchanger (field mx).
Curious about this? Check any message in your inbox and take a look at the header (see source option), you may find a Received-SPF: header if this email has passed an SPF validation.