It means one or more authoritative name servers is misconfigured.  You
can use NSLOOKUP or DIG to find out which one and/or you can try to find
the hostmaster (and then if they are are not at the same "broken" site)
e-mail them.
 
Of course you can prevent future auto-deletes by reconfiguring your list
(but I don't recommend it).
 
Broken DNS configs and/or mailers occur all the time on the Internet.
That's the price you pay for open systems: too many fingers (unwashed
;-)) in the pie.
 
In this particular case, a DNS definition for e-Mail hostB that is used
to "eXchange" (mx) mail for hostA could not be "resolved" for the IP
address of hostB since it was not placed in the DNS.
 
It's sortof/kinda like forwarding your office telephone to your home
phone, but programming a non-existant home number.  Your caller rings
you (perhaps via speed dial) like they always do, but then get a telco
intercept that says your number is not in-service.
 
--  co-owner INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
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