earthlink users problem

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From: RP (rp_at_nospam.com)
Date: 09/01/04 

Date: Wed, 1 Sep 2004 16:55:45 -0400

Hi all, our users were unable to email earthlink.net recipients. After contacting their tech support, they replied as follows. I want to know if it is safe to run the command they suggest for Exchange (highlighted in bold). We are running SBS03 Premium. thanks!

The information below is of a technical nature and you may wish to forward
this to your mailserver administrator in the event that you do not fulfill
that role yourself.

Our engineers have informed us that the error you are receiving:

550-EarthLink does not recognize your computer ([IP]) as connecting from
an EarthLink connection. If this is in error, please contact technical
support.
550-relaying to <********@earthlink.net> prohibited by administrator

..is due to an improper MTA configuration with the host that is
responsible for delivering outbound mail on your network. In a nutshell,
the mailserver which attempted to deliver mail to the earthlink.net e-mail
address was initially unable to successfully deliver the mail to the
earthlink.net MX (more than likely due to high load on our end; no
EarthLink MX host was available to accept the transaction at the moment of
the delivery attempt), and so the EarthLink 'A' record was attempted by
the sending mailserver. The earthlink.net 'A' record, however, forwards
port 25 connections to our outbound SMTP servers. Unless the mailserver
attempting the transaction maintains IP connectivity through the EarthLink
network, delivery attempts through the 'A' record will consequently fail
and the above quoted error message will be returned.

The behavior exhibited by the sending mailserver, in this case, is not
standard. According to RFC 2821, "Address Resolution and Mail Handling":

  "If one or more MX RRs are found for a given
   name, SMTP systems MUST NOT utilize any A RRs associated with that
   name unless they are located using the MX RRs; the "implicit MX" rule
   above applies only if there are no MX records present. If MX records
   are present, but none of them are usable, this situation MUST be
   reported as an error."

Currently the EarthLink.net mx record resolves as follows:

mx4.earthlink.net
mx5.earthlink.net
mx6.earthlink.net
mx7.earthlink.net
mx8.earthlink.net
mx9.earthlink.net
mxa.earthlink.net
mxb.earthlink.net
mxc.earthlink.net
mxd.earthlink.net
mxe.earthlink.net
mx1.earthlink.net
mx2.earthlink.net
mx3.earthlink.net

You may wish to verify that you are able to successfully resolve this
record through your nameservers, and that you can successfully route to
these hosts.

It has been reported that some mailservers behind firewalls which do
not allow transfer of UDP packets larger than 512 bytes may not be
able to return the MX record for earthlink.net. For more information,
please see:

http://support.microsoft.com/default.aspx?scid=kb;en-us;828263&Product=winsvr2003

Our engineers have informed us, however, that the byte size of
our MX record is under the 512 byte limit and is within an RFC
compliant range. If your firewall restricts UDP packet transfers
though, you may want to verify that it will allow transfer of a
MX record within the size limitations specified by RFC1035:

http://www.faqs.org/rfcs/rfc1035.html

Microsoft Exchange users have reported to us that a Windows 2003 server
has included Extension Mechanisms for DNS (EDNS0) to allow larger
packets. If you run this command on a 2003 server: "dnscmd Server
Name/Config /EnableEDnsProbes 0", it fixes it without making any changes
to the firewall.

Assuming that the earthlink.net MX is resolvable, however, our
engineers have informed us that if the sending mailserver cannot
immediately establish a connection to deliver the intended e-mail, the
MTA should attempt to retry a connection to the EarthLink MX, rather
than defaulting to the earthlink.net 'A' record or smtp.earthlink.net.
If, upon review of your mail, you believe that your report
should be personally reviewed by an Abuse staff member,
please reply to this message. Include this entire text and
your original message located below. When resubmitting
reports, please include a brief explanation as to why
resubmission was necessary. When we receive your
resubmission with this message included, we'll investigate
the matter and use it to further refine our filters.

Relevant Pages

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