anonymous mail from Netscape

[Gary Finley <gfin@psych.ualberta.ca>]

Dear zmailers:

I have a number of public-access PCs on my network which have  
Netscape installed.  Netscape has a menu entry for "Mail Document",  
that allows the user to send SMTP mail to a specified server.  The  
program's Preferences window lets the user enter his email address.

Since the user can just fill in whatever address he feels like  
using, this is about the easiest way in the world to send abusive  
mail anonymously, or to send a message that looks like it comes from  
someone else.

I'd like to know if there's a way that smtpserver could be   
configured to plug this barn door that Netscape has opened into my  
mail system's security.  Rejecting mail from certain hosts would be  
a start, since all legit mail from the PCs goes through one of my  
NeXTs via POP service (password secured) or via Pine in a Telnet  
login.

I hesitate to admit this, but I'm still running version 2.21.  It's
been working like a champ for almost 2 years, and I've had no reason
to upgrade.  I'm from the "ain't broke" school of software management.