How to interface a front-end to a MTA?

I've got a nice front-end which I've been using for
years, to access the Inet via a moden and my ISP.
Because of email SendAuthorisation problems, at
the ISP side, I want to 'route' via a linux MTA.

P.E. wrote:-
> The tunnel works well now and is described here.
> http://carnot.yi.org/NetworksPage.html

OK I fetched that with the 2 substantial daigrams,
but it details mostly just the 'configuration' for
someone who already knows the principles.

At this stage I lack basic knowledge of networks.
Eg. my idea of setting Oberon.Text to replace the
<smtp.URL> which was designed for a RS232 -> modem
output, is simplistically absurd.

AFAIK, on *nix machines any one IP-port can communicate
with any other active one, if the configuration allows?
And the ISO-stack allows an application to 'communicate'
down to the 'IP-port' level.

So, for ETHO to communicate with the MTA, the ETHO
application would need to communicate with the ISO-stack.

But LEO currently only talks with the modem, and
only at the ISP is tcp/ip interfaced?

OTOH if I used a network-card, the appropriate ETHO
facility [and presumably also for LEO] would communicate
in tcp/ip ONLY at the output of the card.

That's not what I need, for LEO to communicate with
the *nix MTA.

Apparently ETHO-VNC is related to this matter,
because that also communicates INTERNALLY [on the one
same machine] from ETHO to some port/s via tcp/ip?

I want to understand the higher-level theory before I start
'just editing config files'.

Thanks,

== Chris Glur