Subject: Suggested Clarification to Sect 5 last Para

From: Randall Gellens <[email-masked]>
Date: Wed, 9 Dec 1998 13:37:13 -0500

> If there are no records left at that point, it is an error
> condition, and the message MUST be returned as undeliverable.

If there are no records left at that point, unless the server has 
specifically configured to route or otherwise handle such messages, 
it is an error condition, and the message MUST be returned as 
undeliverable.  Note that
servers MUST NOT at that point attempt to use the A record for the 
destination as an MX record.

---

From: [email-masked] (Kai Henningsen)
Date: 12 Dec 1998 18:12:00 +0200

> specifically configured to route or otherwise handle such messages,

s/such message/messages for those destinations/

> destination as an MX record.

Except for the case where they know the destination, of course, then it  
might be sensible.

I think the important point here is that differing behaviour is OK for  
specific destinations, but not as general behaviour.

MfG Kai

---

From: John C Klensin <[email-masked]>
Date: Sun, 13 Dec 1998 16:11:31 -0500 (Eastern Standard Time)

>...

> specific destinations, but not as general behaviour.

I think this may be backwards, and both suggestions confuse me a
bit.  As I understood it from last week's discussion...

  * We intend to permit "last-resort host" or "smarthost"
    behavior in which, when standard MX resolution fails, things
    are forwarded to a host that is presumed to be smarter than
	the local one about resolving addresses and sending mail
	(or otherwise disposing of it) that is not otherwise
	deliverable.  This is a generic action, not a specific one.

  * When a host is listed in an MX record for a particular
    destination, it is expected to know what to do with the
	mail.  Options can include sending to a better-preference MX
	host or any destination-specific action including routing
	the mail outside the SMTP environment.

  * When all of the MX records for a destination are exhausted,
    it is an error.  The local host can forward the message to a
	generic "smarthost" (as above), but must not play heuristic
	games in the DNS (or otherwise) to try to figure out where
	to send the mail.

  * We do not intend to encourage (or permit) hosts that are not
     in the MX path to intercept messages and apply their own
	 interpretation of what should be done with them.  While
	 that might be necessary in some situations, those actions
	 are considerably outside the scope of the standard.

Now, is that what everyone else thinks we have agreed upon?

    john

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From: "D. J. Bernstein" <[email-masked]>
Date: 13 Dec 1998 22:46:50 -0000

> Except for the case where they know the destination, of course, then it  

Indeed. The spec should explicitly say that none of the MX requirements
apply to computers that have other delivery instructions from the target
domain's owner. From http://pobox.com/~djb/proto/im/remote.html:

                 Moving a message closer to a remote recipient

   For each domain, there are some computers---usually just one---with
   detailed instructions from the domain's owner on how to deliver
   messages to various addresses in that domain.

   All other computers follow the general procedure described here. Each
   host has a distance from the domain; the strategy is to transfer
   responsibility to a host whose distance is smaller.

---Dan