getting mail to work

Jeffrey Goldberg jeffrey at
Wed Mar 14 04:05:51 UTC 2007

On Mar 13, 2007, at 8:17 PM, jekillen wrote:

> On Mar 12, 2007, at 5:14 PM, RW wrote:

>> Just as long as you understand the distinction between forward and
>> reverse DNS. Based on the whois record for for your IP address, at  
>> the
>> moment you appear to have the following reverse DNS for the address
>> range -
>> $ for i in `jot  8 224` ; do dig +short -x 75.7.236.$i  ; done

> OK, It appears that it is the ISPs name servers who
> are responding. When I call up my sights I get to the
> machines they are on according to my present
> DNS setup.

But that is what the public sees.  If (which I strongly doubt) your  
own internal nameservers give a different result to

$ dig +short -x

then it still makes no difference to the rest of the world which,  
when doing a *reverse* lookup on your IP address doesn't get anything  
that looks like your domain name.

> try

That's not the question.  RW was (correctly) talking about *reverse*  
DNS, aka DNS PTR records.  That is we are looking at the translation  
*from* number *to* name.

If you look up one of my statically IP addresses

$  dig +short -x

you get that instead of

It took me many unpleasant hours on the phone to Verizon to get the  
reverse look up the way it is now.  I spent those hours on the phone  
specifically because I did want to run my own direct to MX mailserver.

My mailserver sends out mail as being from  
(in the envelope and header froms) but identifies itself as

a regular look up of either of those returns

A reverse of that turns up

which when you do a regular lookup gets you

So my machine is claiming to be in, and doing a reverse  
lookup on its IP address points you back to  So that  
strongly suggests that when it identifies itself as, it  
is doing so with the consent not only of the person who controls the domain, but also with the consent of the person (in this  
case Verizon) who controls the IP address of the machine.

If mail from my machine failed this IP --> name1 --> IP --> name2 -->  
IP test (the test being that name1 and name2 are in the same domain  
and that "IP" is the same IP throughout), then mail from my machine  
would get a high spam score by most systems.

I really don't want to sound harsh with this, but if you aren't fully  
clear  on concepts like reverse and forward DNS and authoritative  
servers for each, you really should be looking for a solution that  
doesn't involve you running a direct to MX system.  You can still run  
your own mailserver which you can integrate with your webserver, but  
have it relay all of the outgoing mail to your ISP's SMTP host which  
is set up for the purpose.

Also if you post your queries to the postfix mailing list (I think I  
recall that you were using postfix) you will probably find lots of  
pointers to information explaining about configuration.  "The Book of  
Postfix" (ISBN 1-59327-001-1) has a good discussion of the need for  
other hosts being able to reverse resolve the IP of your mail hub.


Jeffrey Goldberg              

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