You have a letter, I have empirical evidence. I suppose I could just be doing it wrong.
220 sbcsmtp3.sbc.com ESMTP Fri, 2 Jul 2004 06:53:59 -0700 (PDT) ehlo no.such.domain 250-sbcsmtp3.sbc.com Hello [66.219.55.2], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 16000000 250-DSN 250-ETRN 250-DELIVERBY 250 HELP mail from: [EMAIL PROTECTED] 250 2.1.0 [EMAIL PROTECTED] Sender ok > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:bounce- > [EMAIL PROTECTED] On Behalf Of Tim Vander Kooi > Posted At: Friday, July 02, 2004 8:47 AM > Posted To: swynk > Conversation: MX records and Reverse DNS lookup > Subject: RE: MX records and Reverse DNS lookup > > I have a letter in hand from SBC stating that they do in fact filter based > on rDNS and the HELO. We don't use them as a provider and we do have a > static address as a part of our own class C. They DID reject all mail in > to multiple clients that we have who are hosted by SBC. We were unable to > send to them until our HELO and rDNS records matched. You can talk > hypothetically all day long. We've been living the reality of it for the > past 2 weeks. > > -----Original Message----- > From: Chris Scharff [mailto:[EMAIL PROTECTED] > Sent: Thursday, July 01, 2004 6:01 PM > To: Exchange Discussions > Subject: RE: MX records and Reverse DNS lookup > > > No need to give them a buzz, they aren't blocking on that criteria. A > quick test reveals that SBC does not block if the ehlo string does not > match the rDNS record. They do however block addresses they determine to > be dynamic. > > There's more than one way to determine that. > > Some people use a regex to determine that based on the PTR of connecting > host. In this case dsl.*.swbell.net is probably sufficient to kick off > that filter. A PTR of some.host.other.than.what.i.ehlo.com would > probably not result in a rejection. > > If SBC or some other host is using netblocks to determine their > filtering, whether or not my PTR matches my EHLO is also not relevant as > the netblock of my server does not change. If they were blocking on this > criteria I'd need either a static IP or to relay though a smart host. My > PTR/EHLO parings aren't a factor. > > > set q=mx > > sbc.com > Server: dns1.austtx.sbcglobal.net > Address: 151.164.20.201 > > Non-authoritative answer: > sbc.com MX preference = 50, mail exchanger = tspsmtp8b.sbc.com > sbc.com MX preference = 60, mail exchanger = sbcsmtp5.sbc.com > sbc.com MX preference = 70, mail exchanger = sbcsmtp3.sbc.com > sbc.com MX preference = 40, mail exchanger = sbcsmtp1.sbc.com > sbc.com MX preference = 40, mail exchanger = sbcsmtp2.sbc.com > > 220 sbcsmtp2.sbc.com ESMTP Thu, 1 Jul 2004 17:45:07 -0500 (CDT) > ehlo clownpenis.fart > 250-sbcsmtp2.sbc.com Hello adsl-68-92-150-59.dsl.austtx.swbell.net > [68.92.150.59 > ], pleased to meet you > 250 ENHANCEDSTATUSCODES > mail from: [EMAIL PROTECTED] > 550 5.0.0 SBCIS Dynamic IP - Access denied > > > -----Original Message----- > > From: [EMAIL PROTECTED] [mailto:bounce- > > [EMAIL PROTECTED] On Behalf Of Tim Vander Kooi > > Posted At: Thursday, July 01, 2004 5:10 PM > > Posted To: swynk > > Conversation: MX records and Reverse DNS lookup > > Subject: RE: MX records and Reverse DNS lookup > > > > Feel free to give SBC a buzz and give 'em a piece of your mind. I'm > not in > > favor of the rule...simply letting the person who started the thread > know > > what the new rules are for some ISPs. We're all allowed to not like > the > > rules all we want, we still have to play by them as long as they > exist. > > > > -----Original Message----- > > From: Chris Scharff [mailto:[EMAIL PROTECTED] > > Sent: Thursday, July 01, 2004 4:52 PM > > To: Exchange Discussions > > Subject: RE: MX records and Reverse DNS lookup > > > > > > An rDNS entry isn't needed to figure out who is responsible for a > > particular IP address. It's also non-RFC compliant. > > http://www.rfc-ignorant.com/ ought to add a category for hosts which > > reject mail as a result. > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Tim > > Vander Kooi > > Posted At: Thursday, July 01, 2004 2:44 PM > > Posted To: swynk > > Conversation: MX records and Reverse DNS lookup > > Subject: RE: MX records and Reverse DNS lookup > > > > It will stop all the "make $0.25 working from home by sending out > spam" > > spammers, because they have no control over their rDNS records. It > also > > now provides a level of "trackability" to the message. As a recipient, > I > > now know where the message originated. I can complain to the ISP > > providing the spammers service, and with enough people being vocal > about > > it the ISP can shut them down. > > > > -----Original Message----- > > From: Ken Cornetet [mailto:[EMAIL PROTECTED] > > Sent: Thursday, July 01, 2004 1:48 PM > > To: Exchange Discussions > > Subject: RE: MX records and Reverse DNS lookup > > > > > > No, it isn't simple if you have multiple outbound SMTP servers that > are > > being NAT'ed through one IP address. > > > > Besides, this check won't stop spam. As soon as this check becomes > > common-place, spammers (and spam zombies) will just start sending the > > "correct" HELO string. > > > > Our SMTP HELO host does not match the reverse lookup of the public IP > > address of our firewall, and I only have about 1 problem site per > year. > > A quick conversation with the site admin usually reveals that they are > > getting lots of complaints about reject email from many domains. As > soon > > as I point out that they are not RFC2821 compliant, they remove the > > check. > > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Tim > > Vander Kooi > > Sent: Thursday, July 01, 2004 11:55 AM > > To: Exchange Discussions > > Subject: RE: MX records and Reverse DNS lookup > > > > > > SBD does it now. So if you have yours setup in a way that doesn't > > conform you're going to start having a good sized chunk of mail not > > reach it's intended recipient. And it's just going to get worse over > > time. It's very simple to set an rDNS entry that matches your HELO > > though, so I'm not sure it's a huge deal. Just something that all > > Exchange and Network admins need to be aware of. > > > > -----Original Message----- > > From: Ken Cornetet [mailto:[EMAIL PROTECTED] > > Sent: Thursday, July 01, 2004 11:37 AM > > To: Exchange Discussions > > Subject: RE: MX records and Reverse DNS lookup > > > > > > To all who consider rejecting an SMTP connection based on what's in > the > > HELO command, you WILL start rejecting valid email: > > > > If you reject connections based on no PTR record for the connecting > IP, > > you will reject a little valid email. If you reject based on the PTR > > record not matching the host name in the HELO, you will reject a lot > of > > valid email. > > > > Thus the prophets spoke in RFC2821 verse 4.1.4 > > > > An SMTP server MAY verify that the domain name parameter in the > EHLO > > command actually corresponds to the IP address of the client. > > However, the server MUST NOT refuse to accept a message for this > > reason if the verification fails: the information about > verification > > failure is for logging and tracing only. > > > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On Behalf Of Jim > > Kennedy > > Sent: Thursday, July 01, 2004 10:54 AM > > To: Exchange Discussions > > Subject: RE: MX records and Reverse DNS lookup > > > > > > > > What most of them are doing is looking at the PTR record of the > sending > > IP and compare it to what you announce in your HELO. And making sure > > they match. They do this because it is very effective at weeding out > > zombied machines. The SMTP HELO of the infected machine is not going > to > > match the PTR of the IP. > > > > What they are doing is suggested by the RFC's, but not required. > > > > So this is an easy fix for you. Just look at the PTR of each of your > > public IP addresses that your email servers use. Then go into Exchange > > and adjust the HELO to match. Hopefully you have exchange 2003, it is > a > > really easy fix. It is in the SMTP properties as 'masquerade domain' > > > > JK > > > > > > > > -----Original Message----- > > From: On Behalf Of April Fleming > > Subject: MX records and Reverse DNS lookup > > > > It is my understanding that many email servers will do a reverse dns > > lookup on incoming email to ensure a valid domain when sifting out > spam > > etc. > > > > Thus, I must ensure that my email server which is sending out email > must > > have an MX record so the Reverse DNS lookup will suceed. > > > > What I would like to know is whether the weight given the MX record > will > > affect the reverse dns lookup. If I have email being sent from email > > server 3 (don't ask why, it isn't the point :) and that email server > is > > weighted 15, will the email servers I am sending out to accept the > > email? > > > > Example > > > > MX 5 Email server 1 > > MX 10 Email server 2 > > MX 15 Email server 3 > > > > Thank you! > > > > April > > > > _________________________________________________________________ > > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > > Web Interface: > > > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&text_mode=&; > > lang=english > > To unsubscribe send a blank email to > > %%email.unsub%% > > Exchange List admin: [EMAIL PROTECTED] > > To unsubscribe via postal mail, please contact us at: Jupitermedia > Corp. > > Attn: Discussion List Management > > 475 Park Avenue South > > New York, NY 10016 > > > > Please include the email address which you have been contacted with. > > > > > > > > _________________________________________________________________ > > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > > Web Interface: > > > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&text_mode=&; 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