SPF, which is an abbreviation for Sender Policy Framework, is a verification system that aims at blocking the so-called e-mail counterfeiting. Basically, this means sending some message from one e-mail and making it look like it’s sent from another one with the idea to scam in some manner the person getting it. If the SPF protection is running for a domain name, a record which contains all mail servers authorized to email messages with addresses within the domain is created. The record is saved on all of the DNS servers that route the web traffic across the globe, so they all will identify whether an e-mail message comes from a valid server or not. The check is done at the very first server where the email goes through and in the first case the email message is forwarded, while in the second one it's removed and it never reaches the supposed recipient. Applying SPF records for your domains will prevent all unauthorized people from using your email addresses for malicious purposes.