[exim] [OT] Why att.net has DNS failure?

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Author: Bill Moseley
Date:  
To: exim-users
Subject: [exim] [OT] Why att.net has DNS failure?
Att.net is reporting a DNS lookup failure on a domain I run. I don't
see any problems but just curious if anyone is familiar with issues
with att.net or might have an idea what might be the problem.

A sanity check, if you will.


I host a domain whmoseley.com. One sender can only get mail through
about 1 in 5 tries. Most of the time she gets a bounce:

    From: postmaster@??? (Webmail Postmaster)
    To: ******@att.net
    Subject: Returned mail: User unknown
    Date: Thu, 25 Jan 2007 20:31:17 +0000


    The following addresses had fatal errors:
    *****@whmoseley.com: 550 [PERMFAIL] destination not valid within DNS


Which is not the most helpful message -- "User unknown" in the subject
but the DNS error in the body. And no other info, like what server
had the DNS lookup error.


That message never got to my Exim4 machine. The domain gets fifty or
so other emails a day without any problems. But this one user
consistently has problems.

The only thing odd about that domain is that there's no A DNS record
only an MX -- which shouldn't be a problem.

The dns boxes are on the same sub-net, which is not great, but doesn't
explain why it's only that one sender with problems.

    $ dig mx whmoseley.com. | grep mail
    whmoseley.com.          86400   IN      MX      5 mail.whmoseley.com.


    $ dig a mail.whmoseley.com. | grep 170
    mail.whmoseley.com.     86368   IN      A       63.205.225.170


Or:

    $ host whmoseley.com
    whmoseley.com mail is handled by 5 mail.whmoseley.com.


    $ host mail.whmoseley.com
    mail.whmoseley.com has address 63.205.225.170


Any ideas?




--
Bill Moseley
moseley@???