Rejecting based on DNS Registrar

[John Rowan]

First, this is more a procmail question than a MailScanner one.
I'm running version 4.21-9 on several old RedHat 9 servers.
Please don't tell me RH9 is dead, I know it.  Proprietary apps running
that the software vendor hasn't moved to a later distribution.

With that said, a lot of spam use to be advertising garbage where the
domain name had been registered through RegisterFly.  Now that
that problem was taken care of it seems like a good amount of the 
advertising
junk is being registered through
COMPUTER SERVICES LANGENBACH GMBH DBA JOKER.COM

None of the companies we correspond with use joker.com so I'm looking for
procmail to look in the body of the email to parse any links then see 
whether
the name is registered through joker.com and throw it away.

My problem is that I have very basic procmail recipe knowledge and don't 
know
how to spawn off to dig or whois to see whether joker.com is the 
registrar. 

I went to Barnes & Noble (book store) looking for a procmail specific 
book but
there was none.