sendmail, changing mail addresses

[art wittmann]

I'm looking at adding some rules (I think) to sendmail.

What I want to do is set up sendmail so that when it sees 
a particular address, it appends a string onto it.  Here's
an example:

Send mail gets:

user at dumb.machine.edu

and I want it to change it to:

@smart.machine:user at dumb.machine.edu

My intention is for mail that is addressed to "dumb.machine.edu" to
be send to "smart.machine.edu".  "smart.machine.edu" knows about 
"dumb.machine.edu" and knows how deliver mail to it.  "smart.machine.edu",
is not smart enough to be listed as the primary mx entry though.  Actually,
it's not reliable enough, or known around the network.  

The machine that is running send mail is a sun sparcstation.  I'm a bit
confused about how to write sendmail rules.  Any help is appreciated.

Art (wittmann at engr.wisc.edu)