Undeliverable email

Posted on 2012-08-21
Last Modified: 2012-08-29
I am getting this error when trying to email someone's company email from mine

Diagnostic information for administrators:

Generating server: APOLLO.MCSDOMAIN.COM #550 5.2.1 Mailbox unavailable. No reverse name (PTR) for your sender IP ( ##

Original message headers:

Received: from APOLLO.MCSDOMAIN.COM ([2002:6464:6729::6464:6729]) by
 APOLLO.MCSDOMAIN.COM ([2002:6464:6729::6464:6729]) with mapi id
 14.01.0379.000; Tue, 21 Aug 2012 11:07:58 -0500
From: My Name <>
To: "" <>
Subject: test
Thread-Topic: test
Thread-Index: Ac1/tyDJKM766f3IQVeolqkTczHr3Q==
Date: Tue, 21 Aug 2012 16:07:58 +0000
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes
x-originating-ip: [2002:6464:67ac::6464:67ac]
Content-Type: multipart/related;
MIME-Version: 1.0
Question by:DaveGerke
    LVL 16

    Accepted Solution

    This is because the recipient server cannot perform a PTR record lookup on the public IP of your mailserver.  It appears you have one, since a lookup on your IP resolves to        ""

    It could be that your mail server is identifying itself as something other than the PTR record.  I cannot tell because you don't appear to accept connections on port 25 there.

    At any rate, make sure that your server is identifying itself as "".  If you still have an issue after that, let us know and we can diagnose further.
    LVL 2

    Assisted Solution

    A reverse DNS PTR record must exist for your mail server. This error indicates it is not setup.
    LVL 2

    Assisted Solution


    You should request both to your service provider to add a PTR record. Also if you are managing your mail server, add a few other records into your DNS setup:

    In your forward DNS zone you should add a zone with the name pointing to your mail server name, i.e. '' or ''

    In this zone you should add:
    Start of Authority (SOA) this should point to your primary DNS (tipically your PDC also)
    Name Server (NS) - Your DNS servers and also your mail server;
    Host (A) - pointing to your mail server or servers;

    I would also advise to add SPF records to avoid SPAM issues:
    Text (TXT) - v=spf1 ptr mx:'' ip4:
    (note that the mx record above should point to the correct name)
    If other mail services are being used such as blackberry external services you may also want to add to this record: -all

    This last record should also be added by your service provider.

    Let us know if you need further information.


    Author Comment

    by:DaveGerke points to which is statically NATed to our webfilter. points to which is statically NATed to the exchange server.

    The exchange server is named Apollo and our domain is MCSDOMAIN. The error message states that the generating server was: APOLLO.MCSDOMAIN.COM.

    I added as the FQDN in the properties of the send connector. Does this take hours to update because I still get the error.
    LVL 16

    Expert Comment

    It could take a while to update on the recipient end.  Depends if they cache DNS lookup results, and if so, for how long.  I'd give it a few hours.
    LVL 2

    Expert Comment

    Make also sure that a nslookup to on your internal network is pointing to your Apollo ip address.
    LVL 16

    Expert Comment

    @gfilipe - That wouldn't necessarily be related.  The generating server (apollo) is sending the failure notice based on what it received from the recipient server.  Not any tests that it is doing itself.  A PTR failure would not originate internally.  (Unless there were some severely draconian policies in place)
    LVL 2

    Expert Comment

    @Enphyniti - you are correct, it is a PTR failure in principle. Just made the mentioned as a nice to have and should have mention it that way.

    Author Comment

    My PTR records were incorrect and I had to setup the information in my mail filter. Since all three of you were on the right track, I will divide the points amongst all. Thank you for your help.

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