I routinely do a dnsreport on my domain. Can someone explain to me the following warning and what to do to repair? "Your domain does not have an SPF record. This means that spammers can easily send out E-mail that looks like it came from your domain, which can make your domain look bad (if the recipient thinks you really sent it), and can cost you money (when people complain to you, rather than the spammer). You may want to add an SPF record before October 1, 2004, the target date for domains to have SPF records in place."