Yes, however, note the requirements for rDNS. They don't say that it
must match the EHLO, only that it must have one and that they are going
to be using the Sorbs DUHL. Course I lifted the letter from the web, I
don't have a copy in hand or anything.
....SBC Letter lifted from the web....
In an effort to reduce the amount of spam delivered to our customers, as
of June 11, 2004, we have enabled two spam prevention measures on our
mail servers. We will now reject email from servers that do not have
reverse DNS (rDNS) setup on their IP address or that are listed on a
black list of dynamic IP addresses.
- The Sorbs DUHL (Dynamic User Host List) black list contains IP
addresses, assigned in a dynamic fashion, by an ISP for an Internet
connection. This protocol (DHCP for example) is widely used for those
Internet users who have dial-up, DSL, ADSL and Cable connections. These
types of Internet access users should relay mail through their ISP's
authorized relays. In fact, most of the IP's on this list were actually
supplied to Sorbs by the ISP's who maintain these IP's.
- rDNS checking (PTR record). Each connection made to deliver email to
your domain will have a rDNS check made against the IP. If the IP
address making the connection does NOT have a PTR record, the connection
will be denied. Anyone that wishes to send email to our servers and does
not have a reverse DNS entry for their IP address will need to contact
their Internet access provider to have this setup.
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:bounce-
> [EMAIL PROTECTED] On Behalf Of Ed Crowley [MVP]
> Posted At: Tuesday, July 06, 2004 2:33 PM
> Posted To: swynk
> Conversation: MX records and Reverse DNS lookup
> Subject: RE: MX records and Reverse DNS lookup
>
> They just implemented it, apparently:
>
> http://www.sfgate.com/cgi-
> bin/article.cgi?file=/chronicle/archive/2004/07/02
> /BUG267FIGR1.DTL
>
> Ed Crowley MCSE+Internet MVP
> Freelance E-Mail Philosopher
> Protecting the world from PSTs and Bricked Backups!T
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Tim
> Vander Kooi
> Sent: Friday, July 02, 2004 6:47 AM
> To: Exchange Discussions
> 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
> >
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