Summary: DNS-MX question

From: Larry Chin (
Date: Tue Oct 04 1994 - 16:05:03 CDT

                        ORIGINAL QUESTION

I am having a small "discussion" with the sysadmin that watches over
the DNS maps for our parent domain.

Having read several sources of DNS information ( including the
excellent O'Reilly tome ), I am still at a loss for a definitive answer
to my questions hence I turn to the collective wisdom of the list.

How do wildcard MX records in the parent domain DNS affect mail
delivery for subdomains given that the subdomains are set up to handle
their own mail ?


There are a couple of issues here.

Basically the way that wildcards work is that they take care of anything that
is not EXPLICITLY cited in the DNS maps. Hence if you are going to put in
wildcards you should make sure that you have records for all the nodes that
you want handled in a specific manner, and have the wildcard as a "catch all"
for everything else - ie: the destination is unknown to the nameserver.

In addition you probably want to make the wildcard of a lesser precedence
( delivery attempted to the non wildcard first ) than the wildcard.

In addition if subdomains are delegated via an NS record, then wildcards in
the parent should not affect mail delivery to the subdomain.

Word to the Wise:
Wildcards are a bad idea since the host that is pointed to by the
wildcard MX MUST be able to do something reaonable with every malformed
or incorrect address that is passed to it because of the MX record.

Thanks to:

Dan Schlitt <>
"Bill Kastner" (
John M. Blasik (
Jochen Bern (
Chris Swanson (
Neil W Rickert (
"J. Adams" (
david@srv.PacBell.COM (David St. Pierre)
Darren Reed (

Tue Oct 4 06:48:52 EDT 1994
Larry Chin {} System/Network Administrator
CCH Canadian Ltd. (416) 441-4001 ext. 349


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