It would seem like a nice feature for Sendmail, but do you think it is realistic to assume that everyone would upgrade? I know of many hosts which use "outdated" versions of Sendmail.
The issue isn't so much everyone upgrading (tho ultimately that is an issue) but, rather, everyone cooperating. A spammer or other foul being can return anything they want on a "caller id" request in the current internet. They can send a msg supposedly from "bill@whitehouse.gov" and then when asked for verification say "ayup, it's bill@whitehouse.gov". The only reason caller-id works in the phone system is because it's the sole provenance of the highly regulated (and generally disinterested, as far as lying for you goes) telcos. And truth be told caller-id doesn't work very well even in the telephone system, except inasmuch as you're willing to refuse all unidentified calls. I suppose a scheme like this slows down the hit+run whackamoles who use throw-away dial-up accounts, but only so long as they can't use their own MTA (which they usually can if it's just a straight PPP connection.) I don't think we can get anywhere so long as one spends time addressing suggestions from individuals who admit they don't understand the technology and who clearly have as an agenda to keep taking monthly fees from spammers (the very few worst excepted.) The answer is two-fold: 1. Make the implicit theft-of-service specifically illegal and tortious. In particular, not identifying the source of the spam in the message (see the recently passed Nevada anti-spam law for some good language on this.) Screw technology on this one, if they defraud they go to jail. 2. Let advertisers devise voluntary schemes profitable to all parties involved. -- -Barry Shein Software Tool & Die | bzs@world.std.com | http://www.std.com Purveyors to the Trade | Voice: 617-739-0202 | Login: 617-739-WRLD The World | Public Access Internet | Since 1989 *oo*