George, while Jim has already discredited your view, I will chime in here as well. I am heavily involved in e-mail servers and the war on spam. I can tell you very firmly that it is not standard practice to require a valid RDNS for both the reason that is stated by Jim and others and also for the reason that presence of a PTR means nothing in the war on spam. Just because a sending MTA has a PTR for its IP means didly-squat. Just look at the virus infected home computers and laptops that are acting as robot relays spewing millions (or is it billions now) of spam per day. You know what, probably 90% of them have a PTR record for their IP address. The best anti-spam software are those based on a weighting system. (Guess what, bayes based/type systems are at the root a weighting system.) Generally speaking, those are configured to give no more than 25% of a hard fail weight to the lack of a PTR record, and nothing meaning no negative weight to the existence of a PTR record. John T eServices For You "Seek, and ye shall find!" -----Original Message----- From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Taylor, George Sent: Friday, June 02, 2006 8:05 AM To: exchangelist@xxxxxxxxxxxxx Subject: [ExchangeList] Re: IMF config Hmmm, should I dance around like a god? or do they even dance? :-) I have to disagree with you John. It is standard practice to require a valid RDNS lookup in order to except a piece of mail. Basically all you are doing is verifying that the sender is in fact who they say they are, or should I say the server connecting to your server is who it is advertising itself as. As you say, take a look at the real world: A guy walks into your mailroom wearing a purple shirt with a unibomber emblem and says "Take this package, it's from UPS..." What's your mail clerk going to say? "I'll take it because I don't care who you are, I just take all packages addressed to me..."? I hope not, that's how things get blown up, that's how your email system will get blown up with viruses, spam, threats, etc... If you cannot verify the origin of a piece of mail and you except it anyways, you put yourself at risk, a conscience email administrator is not going to allow that. Just my .02 George Taylor Systems Programmer Regional Health Inc. _____ From: John T (Lists) [mailto:johnlist@xxxxxxxxxxxxxxxxxxx] Sent: Thursday, June 01, 2006 5:07 PM To: exchangelist@xxxxxxxxxxxxx Subject: [ExchangeList] Re: IMF config Andrew, please tell me you are not actually considering doing this. Yes, the big want-to-be Internet God's such as America Off Line block/refuse on no PTR, but that is not practical in the real world as the rest of us know it. Besides, I think America Off Line is just trying to get on Dan Quails' good side, if he has one. John T eServices For You "Seek, and ye shall find!" -----Original Message----- From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Andrew English Sent: Thursday, June 01, 2006 4:05 AM To: exchangelist@xxxxxxxxxxxxx Subject: [ExchangeList] Re: IMF config Is there anyway to get IMF to drop emails that fail reverse lookup? Thanks Andrew