Sender Policy Framework (SPF) is used to validate the senders IP address against an accepted IP address, defined in the record itself (typically a TXT record)
SPF is an attempt to stop forged (or spoofed) email, for example, if an unscrupulous individual sent an email pretending to be from your domain name, the receiver would first check the IP address of the sender, and validate it against the SPF record. If the IP address of the sender is not listed in the SPF record, the mail will be rejected.
As an example, an SPF record may resemble the following:
TXT "v=spf1 ip4:192.168.0.2 -all"
This will allow the sender at IP address, 192.168.0.2 to send emails from that particular domain name.