Changing mail execution to mailx execution ??

[Keith Paul Hageman]

I've recently gotten a UnixPC and am still learning quite a bit but
have resorted to posting this question instead of digging through
lots of manuals.  No flames please.

I have just gotten HDB 3.5 installed with HDB Admin and have
uucp and mail working between my PC and AT&T's system "drutx".
This was an accomplishment in itself.

My question is that when I receive mail while in the UA the envelope
appears at the top of the screen.  When I select this icon, my system 
invokes mail instead of mailx which I have also installed.

How do I change the UA to invoke mailx instead of mail.

NOTE: I'm not fluent in a lot of the terminology used in articles
posted here so I'd appreciate a clear description without buzz words
or better with buzz words if you would take the extra time to explain 
them also.  

I'll take whatever I can get though.

Thanks in advance,
Keith Hageman
drutx!kph!kph
(303) 538-1673