How does SPF work?

SPF is a framework that need to be implement by both side of the email system, the sender and the receiver.

• The sender need add a TXT entry in their DNS entry. This entry allow the sender to specify what host is authorized to send email using it’s domain name. For example,

  sitek.com.au.     TXT     "v=spf1 mx -all"

  This entry in the sitek DNS entry would mean that all sitek.com.au MX host are authorized host to use sitek.com.au domain name to send out email. They are allow to send out sitek.com.au email address’s email. More information on syntax can be found in www.openspf.org.

• When receiver end, receive an email, it will need to check the sender email address DNS entry. If DNS contain SPF entry, check are perform to make sure that the sending host is one of the machine listed in the SPF entry. This prevent spammer from using your domain name to spam email.

We should encourage ourselves and other to implement SPF framework on their domain and mail server to help fight against SPAM. List of SPF implementation on the receiver end from here.