Subject: Re: FWD: Re: To MX or not to MX?

From: John C Klensin <[email-masked]>
Date: Fri, 05 Mar 1999 17:17:43 -0500 (Eastern Standard Time)

On Fri, 05 Mar 1999 18:32:31 +0100 Brad Knowles 
<[email-masked]> wrote:

>     I think we should explicitly state that how MUAs would deliver mail
> to their upstream servers is a private arrangement issue (since, as far
> as we're concerned, they're not truly on the Internet and we're not
> expecting them to do MX resolution), and then we should describe some
> typical private arrangements.

I have no problem with this approach, and actually prefer 
it, if

 -- someone else drafts text to detail the variety of 
     private arrangements.  
 -- there is reasonable consensus behind the approach
 -- no one insists that we try to bend the text so that 
     "private arrangements" are defined as "fully conforming
     behavior.  One or the other.

>     How these guys go about doing their business has been unregulated and
> pretty much undocumented for too long, for us to come along at this late
> stage and try to impose our view of order upon them.

Again, I have no problem with this.  I was under the 
impression that the WG wanted me to explicitly address the 
case _as part of the standard and within the conformance 
rules_ and I wrote strawman text to that end.  So this 
falls into the "be careful what you wish for" category a 
lot more than it falls into the "things the editor really 
wanted to do" one.

>     Now, when it comes to the Message Submission protocol (whatever that
> might be), I think this would be an ideal time to make use of SRV
> records.  But I think this is a matter for a different document, if not a
> different group.

Again, I concur, at least to the extent that I think that 
is the place to start introducing and standardizing some of 
these variations.

      john

---

From: "Woodhouse, Gregory J." <[email-masked]>
Date: Mon, 8 Mar 1999 10:20:56 -0600

Certainly on a large network, such as the VHA network, we do not want mail
from within our domain to go out to the public mail exchangers and, in fact,
this only happens in the case of configuration problems.

I, for one, would be very interested in seeing a clearer distinction between
MTA to MTA protocols and UA to MTA protocols, including rules for the use of
MX recordsx or other routing mechanisms.
---
Gregory Woodhouse
Managed Care - Technical Requirements Team
[email-masked]
+1 415 744 6362

-----Original Message-----
From: Randall S. Winchester [mailto:[email-masked]]
Sent: Saturday, March 06, 1999 1:10 AM
To: John C Klensin
Cc: Pete Resnick; [email-masked]
Subject: Re: FWD: Re: To MX or not to MX?

What is in an MX....

1) I expect everyone outside my domain to use my "published" MX addresses
when sending mail to my domain.

2) Inside my domain I most often do not send or route mail to those
"published" MX addresses. There are strong performance and service reasons
for doing this. I have only so many machines to handle all the mail that
millions of internet hosts may choose to pass my way. I have separate
machines to handle the mail that my domain sends internal and to the
internet. My domain's mail must go through..

3) I consider my domain to include my customers on travel, at home, or
otherwise connecting to my mailservices from other ISP's. I do not expect
them to use the "published" MX addresses, which may be overrun by the
millions of hosts on the internet, but rather those addresses that I can
guarantee will be available when they need to connect back to my/our
domain.

4) (beyond the MUA issue) I run "sendmail -bd" daemons configured to, at
least, listen to localhost:25. Any other sendmail process started on those
machines talks SMTP to localhost:25 (I do not need a setuid binary). Those
machines which do not listen for incoming SMTP connections (the vast
majority) typically forward mail to my domains internal SMTP servers. There
is no need, or desire, to do an MX lookup for any of that. I run 1000
machines this way.

5) When support for authenticated SMTP exists, my "unpublished" (non-MX)
mailservers will use it to insure that 1) can be more tightly controlled.
I see MX's as a requirement for the unauthorized, but it is all SMTP.

I do not know how you want to write or phrase it, but my view on this is;

a) If you have the consent of the responsible party for a given address,
you MAY choose not to use MX lookups when forwarding to it.
Most MUAs and many intra-domain SMTP servers are in this category.

b) If you do not have the consent of the responsible party for a given
address, you MUST use MX lookups when forwarding to it.
Most inter-domain servers are in this category.

>From my perspective, I feel this is a clear take on the issue.

Randall