[net.mail] Local Network Addresses in the Big Dumb World

gnu@sun.uucp (John Gilmore) (08/28/84)

We had the same problem as UCSD.  Our current solution is to use
subdomains internally (eg, I am gnu@l5.sun.uucp) and translate
these to uucp-like addresses when going to the outside world (eg
sun!l5!gnu).  We also accept these forms, if you can get them thru
other peoples' mailers to us:

	gnu@l5
	gnu%l5
	l5!gnu
	l5:gnu
	l5^gnu

In general, people use "gnu@l5" internally, while outside uucp sites
use "sun!l5!gnu" or just "sun!gnu" since our uucp gateway knows where
we all want to get mail anyway.

I'd suggest NOT generating addresses containing "%" when there is an
alternative, "!".  % came into use as a replacement for "@" when RFC822
decreed that you could not have two @'s in an address.  As more sites
start using it, the parsing becomes impossible, e.g. if you get the
address  ucsd!foo!bar%fly   do you send it fly or foo?  You can send
it to fly, assuming that fly connects to foo via uucp, or you can send
to foo, assuming that fly shares an Ethernet with it.  Either way you'll
be wrong half the time.  If all you parsed was "!" (from the left), there
would be no problem.

The set of addresses you accept isn't half as important as the set you
generate as From addresses, since that determines who can respond to you.
Most mail is responses, plus people kind of expect them to work, better
than a path they dreamed up looking at a net map, anyway.