This document sets out some basic info on how to integrate our DNS with SPF (Sender Policy Framework). For more info on SPF, vist

 Standard SMTP

"v=spf1 ~all"

We strongly recommend that you use the -all default mechanism instead of ~all, if possible. This stricter default mechanism will cause any mail coming from IPs not explicitly included in your SPF record to be rejected at it's destination, providing better protection against spoofing.  Prior to switching your SPF to -all you should ensure that your SPF record includes every provider you legitimately use to send mail; that mail will be lost if you do not.