Intelopment asks: "My Domain name has recently been used a lot in the 'Reply' field by some inconsiderate spammer, and my ISP has suggested that I consider using the Open SPF service as a way to stop spammers from using my domain name for in their mail headers field. From what I can tell, it requires the receiving mail server to actually participate in the SPF service, which is where I have my doubts. Does anyone have any experience with this service? Does it work? Are many ISPs using Open SFP?"