I'm not, but I do have a question about it. Is it something that would best be implemented on the MTA to reject fake SMTP servers, or does it have a "maybe" case which would be best handled by a SpamAssassin rule without outright rejecting the mail?
It looks to me like it's similar to SPF but addresses the hostname in the EHLO message rather than the one in the MAIL FROM message. I'm still unclear how the target field in the SRV record is used.
Like SPF, this is an anti-forgery mechanism, not an anti-spam mechanism. But an anti-forgery mechanism makes SURBL more effective.
