why does sendmail default to c18-ss-1-lb.cnet.com when domain is unknown?

[Sharpe, Sam J]

2009/10/8 Bazooka Joe <fastfish at gmail.com>:
> Sry for a OT sendmail question
>
> In my mail queue I have a bunch of email w/ the domain
> c18-ss-1-lb.cnet.com and the status is "Deferred: Connection timed out
> with c18-ss-1-lb.cnet.com."
>
> Each of the email the user mistypes the domain so that it is not a
> resolving domain name. Sendmail replaces the invalid domain with a
> cnet address.  ex thutrang at c18-ss-1-lb.cnet.com.
>
> The confusion comes when the user gets the email bounced back after 5
> days w/ the domain replaced w/ the cnet one.  Then they complain to
> me.

It's probably because they've mistyped the email as <something>.com.com

[sam at samlap ~]$ host fruckaiomowenuerc.com.com
fruckaiomowenuerc.com.com is an alias for c18-ss-1-lb.cnet.com.
c18-ss-1-lb.cnet.com has address 216.239.122.33

CNET owns .com.com and they have a wildcard DNS record, so you need to
complain to them...

-- 
Sam