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From: fair@ucbarpa.Berkeley.EDU.UUCP
Newsgroups: news.admin,news.software.b
Subject: Re: serious problem - mod articles not sent to mailing site
Message-ID: <18289@ucbvax.BERKELEY.EDU>
Date: Mon, 13-Apr-87 02:09:49 EST
Article-I.D.: ucbvax.18289
Posted: Mon Apr 13 02:09:49 1987
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Summary: explanation & fix

This is a slightly abridged version of a letter I sent to Dave Sherman
explaining what is going on with this, and what to do about it.

	Erik E. Fair	ucbvax!fair	fair@ucbarpa.berkeley.edu

From fair Sun Mar 29 09:48:19 1987
To: mnetor!lsuc!dave@seismo.CSS.GOV

OK, here's that explanation you've been waiting for:

In netnews there is this #define called INTERNET.

If you have it on, and a user hits "r" in readnews (or whatever),
the software will take the address found in the "From:" line and
attempt to use that as a mail address. For this to work properly, the
local mailer must understand what to do with an address of the form:

	user@host.UUCP

where "host" is not necessarily one that it speaks directly to (i.e.
it's gotta generate a path to get there). In fact, the local mailer
has to be prepared to deal with just about anything in the "From:"
line, which is a lot to ask, really. This is why the smart mailers for
UUCP land too so damn long to write. Well, that and the fact that we
were relying on volunteer labor.

So you probably do what most people do: you leave #define INTERNET
off. So what happens when a user hits "r" to mail a reply? Well the
"Path:" line is taken, en toto, as the UUCP path to get to the
author. Neat thing about this is that it makes no demands of the local
mailer at all, because the first site in that path will be you, the
second one will be one that you speak directly to (since you trade
news with them) and so on.

OK, with the background firmly in mind, here's the problem:

You're writing a gateway for stuff from the ARPA Internet mailing
lists, and you have this pathological case to deal with:

	foo!bar!blatz!user@gateway.domain

This is some poor schmuck from UUCP land who has mailed in his message
to the mailing list through a random UUCP gateway on the Internet, and
now you have to make this work from a USENET perspective, so what do
you do? Well, the "From:" is easy:

	From: user@blatz.UUCP

But now we have the "Path:" to deal with. Uh, oh. And this is what the
majority of the USENET uses for mail replies. Well, given that the
netnews software won't send the message to his site if you include the
bare UUCP name in the Path:, you tack on a domain name, so that
they're not equal, that is:

	Path: ucbvax!blatz.UUCP!user

rather than

	Path: ucbvax!blatz!user

and you count on the fact that blatz != blatz.UUCP so that this USENET
article will get to site "blatz" (unfortunately, this was not true
for releases prior to 2.11, but it is trivially fixed: remove the "."
character from the NETCHRS definition and recompile).

Now then, given the mechanics of a mail reply with INTERNET off, whose
mailer has to be smart? Why, yours, Mr. Gateway author! After all, what
you send out will eventually come back as mail of the form:

	XQT (rmail blatz.UUCP!user)

All clear?

	Erik E. Fair	ucbvax!fair	fair@ucbarpa.berkeley.edu