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

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.
5 answers Last reply
More about reverse entry mail servers accept
  1. 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.
  2. 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
  3. 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
    >
    >
  4. 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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