? test for DNS records

Primarily as a self-learning exercise, I'm writing a procmail script to 
look at the List-ID: header (RFC 2919)
(Ref: http://ietfreport.isoc.org/idref/rfc2919/)

I would like to do a DNS check for the list specified in this header. 
After parsing the field contents for the list ID to look up, I thought 
the following would work:

:0
*$ ? nslookup ${LISTID}
{
    dns records were found
}
:0 E
{
    dns records were not found (conclusion - fake list = spam/junk, or 
DNS server unavailable)
}

However, the :0 E clause is never executed, even if the command line 
nslookup fails with a "non-existant domain" message.

Any suggestions?

Thanks,
Don



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