Leaving off the From: works fine.  Proper From line is added as the mail
is sent.  I guess I'm reading old documentation and thought these jobs
were meant for users.  Perhaps they use to be.  The "historical"
document about "A description of the Relayed File Distribution feature"
says
 
   "MAIL indicates that the file to  be distributed is a mailfile, to
    be sent  to the MAILER at  the destination node. The  contents of
    the file are proofread and the  "mail origin" is verified so that
    users  cannot send  forged mail.  ..."
 
Users ask about a facility like this from time to time.
I've been curious how to make it safer.