Mailing List Message #103714
From: ֧ԧ֧ ߧ֧ߧܧ <>
Subject: RE: RDNS (Reverse lookup) failure
Date: Mon, 19 Nov 2012 06:47:09 -0800
To: <CGatePro>
X-Mailer: Microsoft Office Outlook 12.0



We had similar issue but due to different reasons. We solved it using dNAT (destination NAT) on our  router.

Our solution is not perfect, but works for us. What we did ? assigned public IP (IP of our mail server the same as in PTR) on the router interface and use dest DNS to our local IP of our natted mail server.


Best regards,






From: CommuniGate Pro Discussions [] On Behalf Of Thomas Bleek
Sent: Tuesday, November 06, 2012 12:10 AM
To: CommuniGate Pro Discussions
Subject: Re: RDNS (Reverse lookup) failure


Your router is NATting the outgoing traffic?


Am 05.11.2012 um 19:05 schrieb Urs Grtzner <>:

Thanks for your help

In fact is inbound and outbound as well. 

Of course, as is the Gateway of our LAN, every mail passes this IP as well. But its origin should be



I do not understand the mechanism, when and how this Gateway IP  is attributed and sent with mail. And why not the mail servers IP???



The weird thing is: before we switched to our new provider this did not happen. Except that Router, IPs and DNS have changed, everything should work analogously.



At the moment I have a workaround, that I can send my SMTP in relay with the SMTP of our Provider Swisscom. This "whiteswashes" the fact, that our reverse is not correct.


But thats not a solution. I want that the is sent with the mail. (The reverse lookup to might help as well but I am not happy with that trick as soon as I did not understand the mechanism) ;-)










Lyle Giese <>


Re: RDNS (Reverse lookup) failure


Mon, 05 Nov 2012 11:06:39 -0600


CommuniGate Pro Discussions <>



It looks to me like is for inbound email, while outbound email is forwarded via does not have a reverse lookup.  This ip address does not appear to be accepting inbound email so I can not verify the HELO/EHLO greeting it may be providing.  

I think you need to get a reverse installed for with the greeting used by that machine.

Lyle Giese
LCR Computer Services, Inc.

On 11/5/2012 10:07 AM, Urs Grtzner wrote:

We have changed our Internet provider, needed to change also the DNS authority and the IP's.


The new zone file on the Master DNS is ok, according to the rules.  


The name Server IPS on the Server are changed to the new provider.


Our server is behind a Firewall, with local IPs,,



The forward and reverse lookup for and the public IP are OK (see lookups below)








Now we have the following problem:


When sending mails its not the IP of our server which is transmitted, but the IP of our Gateway. Of course the RDNS lookup will fail for servers, which perform this check. 



I do not know how this IP is forwarded with mail. How does the mail server get his own public IP? By checking the DNS?  I don't understand how the gateway IP is coming into the header



Any help is appreciated







PS: Here is a mail I have sent from the concerned server One can see the gateway number as the origin, instead of the mail servers IP number




Von:  Urs Grtzner <>

Betreff:  test WAN IP

Datum:  5. November 2012 12:47:33 MEZ

An:  Gruetzner Urs <>

Return-Path:  <>

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„Lookup wurde gestartet



; <<>> DiG 9.6-ESV-R4-P3 <<>> any +multiline +nocomments +nocmd +noquestion +nostats +search

;; global options: +cmd 3600 IN MX 10 3600 IN A

2012103001 ; serial

10800      ; refresh (3 hours)

3600       ; retry (1 hour)

604800     ; expire (1 week)

21600      ; minimum (6 hours)

) 687 IN NS 687 IN NS 687 IN NS 687 IN NS 687 IN A 19862 IN A 1833 IN A




„Lookup wurde gestartet



; <<>> DiG 9.6-ESV-R4-P3 <<>> any +multiline +nocomments +nocmd +noquestion +nostats +search

;; global options: +cmd 657 IN A 657 IN NS 657 IN NS 19832 IN A 1803 IN A



„Lookup wurde gestartet



; <<>> DiG 9.6-ESV-R4-P3 <<>> -x any +multiline +nocomments +nocmd +noquestion +nostats +search

;; global options: +cmd 86400 IN PTR




Dr. Thomas Bleek, Netzwerkadministrator
Helmholtz-Zentrum Potsdam
Deutsches GeoForschungsZentrum
Telegrafenberg A20/225
D-14473 Potsdam
Tel.: +49 331 288- 1818/1681 Fax.: 1730 Mobil: +49 172 1543233


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