Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1+some 2/3/84; site dual.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!houxm!ihnp4!dual!fair From: fair@dual.UUCP (Erik E. Fair) Newsgroups: net.mail Subject: Re: user@system.arpa syntax question Message-ID: <494@dual.UUCP> Date: Wed, 9-May-84 05:41:15 EDT Article-I.D.: dual.494 Posted: Wed May 9 05:41:15 1984 Date-Received: Wed, 9-May-84 23:46:20 EDT References: <390@rdin.UUCP> <472@dual.UUCP> <1748@mit-eddie.UUCP> Organization: Dual Systems, Berkeley, CA Lines: 49 > From: gds@mit-eddie.UUCP (Greg Skinner) > > But Erik: Will seismo's sendmail.cf automatically convert the address > to the right of seismo to an arpa-style address just because the '@' is > there? Does that mean if seismo's ARPAnet service is disabled the > message will lose? (I hope sendmail.cf has info to do routing in the > presence of the higher-precedenced-network failure, but I haven't looked > at it yet to know.) >> floyd!harpo!seismo!hao!hplabs!sri-unix!reiher@ucla-cs.arpa Remember that UUCP mail works by stripping off the machine names as it goes. So when the letter gets to seismo, uuxqt executes a command like this: rmail hao!hplabs!sri-unix!reiher@ucla-cs.arpa reduced to simplest form, you now have a problem, which you had all along, but didn't know about until you hit a site that understands what `@' means. This problem in short is, `How do you parse a!b@c?' (a!b) @ c (Hello C.ARPA, I've got a letter for ) a! (b@c) (uux - a!rmail b@c) Ambiguity. In the UUCP world, this is easy. Bangs come first, (form #2) becase we don't know about at signs and ARPANET and RFC822. In the ARPANET world, anything to the left hand side of an `@' is for local interpretation by the host listed on the right hand side of the `@'. When you hit an ARPANET site, this rule come first, unless you force things, which I won't go into here. So when the address listed above gets to seismo, it will open a TCP socket to UCLA-CS.ARPA, and say, RCPT and UCLA-CS will say, 550 Huh? Whodat? Seismo will thank the nice smtp server, and mail a letter back to original sender saying it was unable to deliver it. Nope, no rerouting to UUCP, because ARPANET failed, at least not by default. Erik E. Fair ucbvax!fair fair@ucb-arpa.ARPA dual!fair@Berkeley.ARPA {ihnp4,ucbvax,cbosgd,decwrl,amd70,fortune,zehntel}!dual!fair Dual Systems Corporation, Berkeley, California