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no reverse DNS entry; some mail servers may not accept you..

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Anonymous
October 29, 2004 6:18:02 PM

Archived from groups: microsoft.public.exchange2000.general,microsoft.public.win2000.dns (More info?)

Couple of users have experienced NDR (non-delivery reports) to a couple of
domains.
I suspected it was down to us been listed in a spam blocklist, after doing a
spam database lookup at http://www.dnsstuff.com i found the very first
record shows the public IP address of our exchange server - "PTR -
MISSING -- abc.xxx.yyy.zzz has no reverse DNS entry; some mail servers may
not accept your mail"

Here's a snip of a NDR to one of the addresses:

The following recipient(s) could not be reached:

someone@someuni.ac.uk on 29/10/2004 14:00
The destination system is currently not accepting any messages.
Please retry at a later time. If that fails, contact your system
administrator.
< mailsweeper.LOCAL #5.3.0>

What cause of action should I take to fix the delivery failures, what
options do I have, thx.
Anonymous
October 29, 2004 6:18:03 PM

Archived from groups: microsoft.public.exchange2000.general,microsoft.public.win2000.dns (More info?)

Leon wrote:
> Couple of users have experienced NDR (non-delivery reports) to a
> couple of domains.
> I suspected it was down to us been listed in a spam blocklist, after
> doing a spam database lookup at http://www.dnsstuff.com i found the
> very first record shows the public IP address of our exchange server
> - "PTR -
> MISSING -- abc.xxx.yyy.zzz has no reverse DNS entry; some mail
> servers may not accept your mail"
>
> Here's a snip of a NDR to one of the addresses:
>
> The following recipient(s) could not be reached:
>
> someone@someuni.ac.uk on 29/10/2004 14:00
> The destination system is currently not accepting any
> messages. Please retry at a later time. If that fails, contact your
> system administrator.
> < mailsweeper.LOCAL #5.3.0>
>
> What cause of action should I take to fix the delivery failures, what
> options do I have, thx.

Contact your ISP (whomever owns your public IP block) and ask them to create
the reverse-lookup record.
If they won't, can't, or that doesn't resolve your problem, you could set up
an SMTP connector that forwards Internet mail to your ISP's SMTP server for
delivery, rather than sending out directly from exchange.
October 29, 2004 7:48:00 PM

Archived from groups: microsoft.public.exchange2000.general,microsoft.public.win2000.dns (More info?)

<snippage>
> What cause of action should I take to fix the
> delivery failures, what options do I have, thx.

To explain it in "clear"; let's assume you own
the domain "foobar.com" and you have a mail
server "mail.foobar.com" which is the primary
MX for the domain; this server has an address
of 1.2.3.4; now

some mail servers perform a reverse lookup
on the incoming connections and check if the
"helo" string matches the reverse DNS name
this means that if your server connects to the
SMTP server ad 5.6.7.8 and starts an SMTP
session it will send out something like

HELO mail.foobar.com

now, the server at 5.6.7.8 has the "reverse DNS
lookup" enabled, so it will issue a reverse lookup
for 4.3.2.1.in-addr.arpa; at this point, if the DNS for
foobar.com is correctly configured the answer to
such a query should be

mail.foobar.com

it that's not true, the mailserver at 5.6.7.8 will just
refuse any mail from your server at 1.2.3.4 since
the HELO id-string doesn't match the reverse DNS
lookup result

to solve this issue; given you don't own the IP block
1.2.3.x you should talk to your ISP or carrier and ask
them to create an entry in their DNS for your mailserver
so that 4.3.2.1.in-addr.arpa will resolve to mail.foobar.com
on the other side, if you own the IP block it will be just a
matter of creating the correct entry into the reverse zone

hope it's clear; if not, feel free to ask

Regards


--

* ObiWan

Microsoft MVP: Windows Server - Networking
http://mvp.support.microsoft.com
http://italy.mvps.org
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Anonymous
October 29, 2004 7:48:01 PM

Archived from groups: microsoft.public.exchange2000.general,microsoft.public.win2000.dns (More info?)

Thx for your input guys much apprecitaed.
I will get in contact with my isp to see whteher reverse loookup is
something we can have on the IP address.
thx again.

"ObiWan" <obiwan@mvps.org> wrote in message
news:uvfTp3bvEHA.1292@TK2MSFTNGP10.phx.gbl...
> <snippage>
> > What cause of action should I take to fix the
> > delivery failures, what options do I have, thx.
>
> To explain it in "clear"; let's assume you own
> the domain "foobar.com" and you have a mail
> server "mail.foobar.com" which is the primary
> MX for the domain; this server has an address
> of 1.2.3.4; now
>
> some mail servers perform a reverse lookup
> on the incoming connections and check if the
> "helo" string matches the reverse DNS name
> this means that if your server connects to the
> SMTP server ad 5.6.7.8 and starts an SMTP
> session it will send out something like
>
> HELO mail.foobar.com
>
> now, the server at 5.6.7.8 has the "reverse DNS
> lookup" enabled, so it will issue a reverse lookup
> for 4.3.2.1.in-addr.arpa; at this point, if the DNS for
> foobar.com is correctly configured the answer to
> such a query should be
>
> mail.foobar.com
>
> it that's not true, the mailserver at 5.6.7.8 will just
> refuse any mail from your server at 1.2.3.4 since
> the HELO id-string doesn't match the reverse DNS
> lookup result
>
> to solve this issue; given you don't own the IP block
> 1.2.3.x you should talk to your ISP or carrier and ask
> them to create an entry in their DNS for your mailserver
> so that 4.3.2.1.in-addr.arpa will resolve to mail.foobar.com
> on the other side, if you own the IP block it will be just a
> matter of creating the correct entry into the reverse zone
>
> hope it's clear; if not, feel free to ask
>
> Regards
>
>
> --
>
> * ObiWan
>
> Microsoft MVP: Windows Server - Networking
> http://mvp.support.microsoft.com
> http://italy.mvps.org
>
>
October 29, 2004 9:02:15 PM

Archived from groups: microsoft.public.exchange2000.general,microsoft.public.win2000.dns (More info?)

<snip>
> Contact your ISP (whomever owns your public IP block) and ask them to
> create the reverse-lookup record.
> If they won't, can't, or that doesn't resolve your problem, you could set
> up an SMTP connector that forwards Internet mail to your ISP's SMTP server
> for delivery, rather than sending out directly from exchange.

Another solution (although I can't say I really like it) would be
setting up the mailserver so that it will announce itself as.......
"4.3.2.1.in-addr.arpa" this way the reverse lookup should work
as well ... although as I wrote above this isn't exactly the best
solution around ... but just a quick & temporary "hack" :-)

Regards

--

* ObiWan

Microsoft MVP: Windows Server - Networking

http://mvp.support.microsoft.com
http://italy.mvps.org
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