Re: FW: Returned mail: User unknown

[Richard Welty <rwelty@xxxxxxxxxxxxxxxxxxxxxx>]

At 11:02 AM 8/28/98 -0400, Bill Bain <bbain@domain.elided> wrote:
>Well, speak of the devil.  Looks like my reply bounced.  thanx for your
>help.

i'm sending this to the entire list for instructional purposes; this is not
alfa related but is directly relevant to the changing climate of the
internet, where the spam problem is becoming so severe that traditional
email communications are increasingly broken (see http://www.cauce.org,
familiarize yourself with all current legislation before congress, and
write your congressman. today!!!!!)

bill's corporate firewall configuration is missing a few parts. as a
result, krusty/digest.net can't identify it, and as part of my spam
defenses we don't talk to unidentifiable hosts.

bill's email passes through a system which calls itself fwgateway.imnet.com
on the way to the outside world, as evidenced by this received: line which
i clipped from his mail header:

Received: from unknown (HELO fwgateway.imnet.com) (206.113.249.2)
  by wizvax.wizvax.net with SMTP; 28 Aug 1998 15:04:33 -0000

wizvax was unable to identify the host, and so noted this when it accepted
the mail. krusty will reject any mail from an unidentifiable host. if i use
the un*x tool nslookup to investigate, i see that yes, the domain name
system doesn't have any identification for fwgateway.imnet.com, either
forward (forward meaning that i can get a numeric ip address, given the
host name) or reverse (meaning that given a numeric ip address, i can get
the host name). here is the pertinent output from nslookup:

$ nslookup
Default Server:  ns1.krusty-motorsports.com
Address:  192.94.170.7

> fwgateway.imnet.com
Server:  ns1.krusty-motorsports.com
Address:  192.94.170.7

*** ns1.krusty-motorsports.com can't find fwgateway.imnet.com: Non-existent
host/domain
> set type=ptr
> 206.113.249.2
Server:  ns1.krusty-motorsports.com
Address:  192.94.170.7

*** ns1.krusty-motorsports.com can't find 2.249.113.206.in-addr.arpa.:
Non-existent host/domain
> 

krusty expects both the forward and reverse lookups to resolve; in this
case both the forward and reverse lookups fail. the most common case is
forward lookup that works, but reverse lookup that fails -- many sysadmins
don't think that reverse lookup is important, but those of us who have
observed a 90% correlation between bogus reverse lookup and spam do
consider it important.

the only person who can truly fix this is the adminstrator responsible for
domain name service at imnet.com

richard

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