What is SPF? SPF is an extension to Internet email. It prevents unauthorized people from forging your email address. But for it to work, you may need to change some settings in your email program. Otherwise, the system may mistake you for an unauthorized person. If your mail was inadvertently blocked by a receiver who uses SPF, read on.

Messages that bounce due to SPF failure should include a URL to this page (or to a page defined by the sender domain in an explanation string).