The hosting Control Panel has been equipped with another tool, designed to give you more control over your domain’s sender policy.
As you may already know, domains use public records (DNS) to direct requests for different services (web, e-mail, etc.) to the computers that perform those services. All domains have e-mail (MX) records to tell the world what computers receive mail for the domain.
SPF stands for Sender Policy Framework, and is an extension of SMTP that stops e-mail spammers from forging the “From” fields in an e-mail. As SMTP itself does not carry an authenticating mechanism, the SPF extension provides the authentication scheme by specifying which computers are authorized to send e-mail from a specific domain. In order to use SPF, the domain sending e-mails must establish an SPF record that is published in the DNS records.
SPF works by publishing “reverse MX” records to tell the world what machines are authorized to send mail from the domain. When receiving an e-mail message, the recipient can check those records to make sure mail is coming from where it should be coming from. This means that the sender domain is compared to the SPF record for that domain to determine if the e-mail sender is indeed authorized to transmit e-mails from that particular address. If the e-mail comes from a domain that is not authorized, the DNS server will disregard the e-mail request. In other words, SPF prevents people from stealing your e-mail addresses and pretending that it is you who send junk/spam e-mail to other people.
Please note that these settings are for advanced users only!
For more detailed information, you may check the Show/Hide Help in the SPF section itself.