Sender Policy Framework
Sender Policy Framework (SPF) is a system to eliminate spam based on the idea that only certain computers should be allowed to send mail for a given domain. SPF allows a domain's owner to specify which hosts may send mail purporting to be from that domain by creating TXT type records in the DNS for the domain. Unlike DomainKeys Identified Mail, only source hosts/addresses may be specified, meaning that should a host/ip address be compromised (such as by Address Resolution Protocol spoofing on an ethernet segment, or system compromise), unauthorized messages may still be sent originating from the given source address and would be accepted based on the SPF record. Any number of hosts may be specified in the TXT record for a given domain, and pointers to SPF records in other DNS zones may be included as well.