Why can't I use UUNET's smail? Smail for Xenix worthwhile?

[Mark McWiggins]

I recently had cause to send E-mail to user "macsmith at athena.mit.edu" on 
ARPAnet for the first time, and since UUNET has smail and I'm directly 
connected, I thought "no problem", it's just:

		uunet!macsmith at athena.mit.edu

But that didn't work.  So I posted a note to comp.unix.questions (the wrong
place, I'm told) asking "How do I send mail to ARPA?" and got back replies

		uunet!macsmith%athena.mit.edu

			and

		uunet!athena.mit.edu!macsmith

			and

		uunet!macsmith%athena.mit.edu.ARPA at UUNET.UU.NET

and one or two others, all of which I tried and none of which
worked.

I don't understand why not.  I thought the idea of smail was to let you
address email by user at site.domain; if I get my mail to uunet, why doesn't
its smail take over from there?  Is there a "precedence" problem; that is, 
does uunet!macsmith always parse as SITE "macsmith"?  And is there a way 
around this?

Even if there is, is there some compelling reason I should be running smail
myself on my single-user 286 Xenix box?  Is there some tweak needed to make
the standard smail distribution work with 286 Xenix?

I had been half-following the 'smail-and-domain-registry' discussion in
comp.mail.uucp not thinking it applied much to me, so ... forgive me if
I'm treading well-worn ground, and thanks in advance.
-- 

Mark McWiggins			UUCP:		uunet!intek01!mark
DISCLAIMER: I could be wrong.	INTERNET:	intek01!mark at uunet.uu.net
						(206) 455-9935