A mail delivery puzzle

[jc at trillian.mit.edu (John Chambers)]

Nathan Meyers wrote:
| On Wed, Sep 18, 2002 at 11:39:57PM -0400, Bill Horne wrote:
| > Now, the problem: I have an MX record in the ampr.org dns, which points to
| > billhorne.homelinux.org, the dynamic dns domain name for my Linux firewall.
| > If I send email from either netscape.net or hotmail, to
| > <user>@w1ac.ampr.org, it gets through OK. I have set the new domain in the
| > sendmail.rc file, so sendmail knows it's supposed to take mail for
| > w1ac.ampr.org (and indeed it does, from hotmail/netscape). However, mail
| > from my attbi.com address produces an error from the attbi.com postmaster,
| > saying that "Host w1ac.ampr.org not found".
|
| I can't find any MX records for ampr.org or w1ac.ampr.org; in fact, I
| can't find any records at all for the latter name. What do netscape.net
| and hotmail know that I don't?

Well, I tried this from several machines:

: host ampr.org
ampr.org has address 44.0.0.1
: host w1ac.ampr.org
w1ac.ampr.org mail is handled (pri=20) by billhorne.homelinux.org
:

I got exactly the same results everywhere I tried it.  So  maybe  the
attbi.com  dns  servers are filtering it out for some reason?  I also
tried a few more detailed commands, all of which worked everywhere. I
wasn't  able  to  get  any failures at all.  And all the replies were
instantaneous (to the human eye).  For example:

: host -v w1ac.ampr.org
Trying null domain
rcode = 0 (Success), ancount=0
For authoritative answers, see:
ampr.org        10695 IN        SOA     ampr.org brian.ucsd.edu(
                        102091907       ;serial (version)
                        36000   ;refresh period
                        3600    ;retry refresh this often
                        7200000 ;expiration period
                        86400   ;minimum TTL
                        )
: