Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!INFOODS.MIT.EDU!KLENSIN
From: KLENSIN@INFOODS.MIT.EDU (John C Klensin)
Newsgroups: comp.protocols.ibm
Subject: Re:      re: e-mail and System/370 Systems Person
Message-ID: <9004111823.AA18618@lilac.berkeley.edu>
Date: 11 Apr 90 14:08:27 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: John C Klensin <KLENSIN@INFOODS.MIT.EDU>
Organization: The Internet
Lines: 37

Jeff,
  I'm going to post this to the list on the theory that the principle, if
not the specific details, may be of general interest (again).

>I'm told that a better form of my e-mail address is as follows:
>    jbeard%quintus.com@sun.com

"quintus.com" is a registered Domain Name System name on the Internet.
This makes the "better" form of your e-mail address (as well as the simple
and obvious one)
    jbeard@quintus.com

Now, where does "sun.com" come in?  At the moment, mail addressed to
quintus.com (as above) from the Internet is sent--automatically, by the
mail sending software--to "sun.com" which acts as a Mail eXchanger for
"quintus.com".  But, users sending mail to you don't need to know that, and
*shouldn't* know and remember that.  Why?  Well, if quintus ever changes
its connectivity, or an additional Mail eXchanger becomes available, this
can be reflected in easily updated (distributed and dynamic) tables,
retaining the name, while use of %quintus.com@sun.com specifies a
connectivity and a routing, which is, in general, a bad idea.

This address should also work from BITNET, as the use of the domain ".COM",
if not found otherwise, will route the mail to a BITNET->Internet gateway.
All of the correctly-functioning ones of those are able to figure out what
to do with "@quintus.com" and do it; any that are not correctly-functioning
should be corrected.

Generalization and moral:  Use addresses of the form user%host@domain only
when absolutely necessary, i.e., when "host" is *not* a registered Internet
domain name.  If "host" is a registered Internet domain name, use of the
user%hostdomain@gatewaydomain form, rather than the user@hostdomain form,
does not add any addressing or performance advantages, and tends to cause
long-term addressing problems as networks and connections evolve.
   --john
   Klensin@MIT.EDU
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