BIG networks

[ron%BRL-TGR at tgr.UUCP]

Sorry, there is nothing inate to ARPA mail that keeps you from getting
"no such user" or "this site is down" messages.  The specification only
deals with two machines talking to each other once the connection is made.
Most systems will tell you that a user doesn't exist during the SMTP dialog.
It is everyones implementation that deals with when retries are done and
what the nature of the error message returned is.  On our system, you can
either send your letter into the mail queues and blindly assume it will
either get there, or you'll get notified eventually, or you can sit there
and watch it try to be delivered to the remote machine immediately.

-Ron