🚀 go-pugleaf

I don't know why I'm putting my foot into this one, but....


An internetwork mail router must, by definition, transform addresses from
one of its networks to addresses that are acceptable to ALL hosts on
its destination network.

The uucp network does not define addresses. Instead, it defines paths
of the form [site!]site!user.  Only the next site in a path need be
known to a uucp sender; as the message traverses the uucp network, each
site discards its hostname from the front of the path and resends the
file to the next site in the path.  There is no address; there is only a
path.

The UUCP Mapping project has attempted (and succeeded, in large part) to
define uucp addresses of the form @host.uucp.  This functions in the
uucp network by replacing the address with a path (usually a path
calculated by picking a least-cost route from the uucp map data).
But the '@'-address is eliminated and replaced by the path, since uucp
does not assign any significance at all to the '@'.

Note that the @ address may remain in the mail headers, but that isn't
significant to the uucp mail network; the headers are NOT used for mail
delivery, although many uucp mail systems will correctly prefix the Unix
header From_ (that's "From ", not the RFC822 "From: ") as the mail is
relayed through them.

Some uucp hosts, particularly those running sendmail, WILL update the
RFC822 "From: " line.  Others don't, which means that the From: line
is of questionable integrity if the mail has ever passed through a uucp
link.

Strictly speaking, an internet-compliant (i.e., it pays attention to
the From: line) mailer receiving mail from uucp should replace the From:
line with the From_ line (since the From: is unreliable), unless the From:
address is a valid domain-style address.  Few sites do this yet.

So, because uucp requires PATHS of the form site!site!user, a
properly-operating internet-to-uucp gateway will transform a From:
address of the form user@domain to domain!user, preserving the domain
unless the domain is ".uucp",  then prefix that with the gateway's uucp
address.  Anything else would require the final destination of the mail
to be able to interpolate or translate addresses, and you simply can't
depend on that capability.

Thus if the From: line is of the form
	user@host.domain
(where 'domain' is NOT "uucp"), then transform the address to
	gateway!host.domain!user
And that's what uunet (and ucsd, and decwrl, and lots of other gateways)
are doing.  It's clearly the right thing to do by default.

Gateway sites which want to go to the trouble of also supporting uucp
"smart" hosts could have a way to leave the From lines alone, on the
declaration that the destination can handle it.  But they shouldn't
DEFAULT that way.
		- Brian