Sender Policy Framework
First of all, SPF is not a service, but rather a specification of how domain owners can publish their policies for using their domains in e-mail traffic, and also a specification of how received mail servers should interpret these policies. SPF is a public standard and therefore free for everyone. Publishing SPF records is done regularly in your own DNS by you or your ISP, or even by your IT department. Checking SPF records for incoming mail is available as a free add-on for most mainstream mail servers such as Sendmail, Postfix and others (except most proprietary mail servers). Many proprietary servers support SPF or have add-ons available.
If you want to know more about it, please contact your dealer or go to the "implementations" page, which we have linked to you. If you need help from a consultant to set up SPF, you are welcome to look at the list we have linked, where you will find some people who can help you.