Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
From: Keith Moore <[email-masked]>
To: "Donald E. Eastlake 3rd" <[email-masked]>
Cc: [email-masked]
Date: Mon, 16 Nov 1998 22:18:03 -0500

> Actually, you can specify the target port in the SRV resource record
> (RFC 2052), which is currently Experimental and more or less ignored
> by everyone.  However, there is a move afoot to put it on standards
> track (draft-ietf-dnsind-rfc2052bis-00.txt).  If that happens and it
> gets widely deployed, then in a few years it might solve your problem.

Yes, but we already have MX.  We don't need SRV for email, and we
certainly don't need the disruption that would result from having
yet another way to find the recipient's mail domain. 

Keith

To: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I send mailto it? 
Date: Fri, 13 Nov 1998 15:47:06 -0500
From: "Donald E. Eastlake 3rd" <[email-masked]>
Sender: [email-masked]

Actually, you can specify the target port in the SRV resource record
(RFC 2052), which is currently Experimental and more or less ignored
by everyone.  However, there is a move afoot to put it on standards
track (draft-ietf-dnsind-rfc2052bis-00.txt).  If that happens and it
gets widely deployed, then in a few years it might solve your problem.

Donald

From:  John C Klensin <[email-masked]>
Date:  Thu, 12 Nov 1998 23:32:00 -0500 (Eastern Standard Time)
In-reply-to:  <[email-masked]>
To:  Alexey Melnikov <[email-masked]>
Cc:  [email-masked]
Message-id:  <[email-masked]>
Content-type:  TEXT/PLAIN; CHARSET=US-ASCII
X-Authentication:  none
Sender:  [email-masked]
Precedence:  bulk
>
>On Fri, 13 Nov 1998 02:31:58 +0300 Alexey Melnikov 
><[email-masked]> wrote:
>
>> > There are also multiple reasons why this would be a bad idea.
>> > They include reintroducing a reason for explicit source routes
>> 
>> Why?
>
>So that one can specify different ports at different hops.  If 
>there is enough requirement for this to introduce a protocol/ 
>syntax change, then there ought to be enough that I might want 
>to use it down a successively-better-preference MX path.  But 
>the DNS can't accomodate different port numbers, so one might 
>want
>  <@host1:port1, @host2:port2, @host3: user@host4:port4>
>note this also points out a little problem with the syntax you 
>suggest.
>
>
>> I am not insisting on using <username>@<server>:<port> syntax.
>> I would like to know how this idea was implemented (if it was) : server is
>> specially configured to connect particular server on non standard port (i.e.
>> the use of configuration files), server uses DNS Well-known service record or
>> Service Location Protocol, other ways.
>
>To the best of my knowledge, this has been done by private 
>client-side (more generally, sender-side) configuration and out 
>of band communication about the ports to use.  There are no DNS 
>or SMTP facilities for specifying funny ports in an address.
>
>   john

Date: Thu, 12 Nov 1998 23:32:00 -0500 (Eastern Standard Time)
From: John C Klensin <[email-masked]>
Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
To: Alexey Melnikov <[email-masked]>
Cc: [email-masked]
Sender: [email-masked]

On Fri, 13 Nov 1998 02:31:58 +0300 Alexey Melnikov 
<[email-masked]> wrote:

> > There are also multiple reasons why this would be a bad idea.
> > They include reintroducing a reason for explicit source routes
> 
> Why?

So that one can specify different ports at different hops.  If 
there is enough requirement for this to introduce a protocol/ 
syntax change, then there ought to be enough that I might want 
to use it down a successively-better-preference MX path.  But 
the DNS can't accomodate different port numbers, so one might 
want
  <@host1:port1, @host2:port2, @host3: user@host4:port4>
note this also points out a little problem with the syntax you 
suggest.

> I am not insisting on using <username>@<server>:<port> syntax.
> I would like to know how this idea was implemented (if it was) : server is
> specially configured to connect particular server on non standard port (i.e.
> the use of configuration files), server uses DNS Well-known service record or
> Service Location Protocol, other ways.

To the best of my knowledge, this has been done by private 
client-side (more generally, sender-side) configuration and out 
of band communication about the ports to use.  There are no DNS 
or SMTP facilities for specifying funny ports in an address.

   john

Date: Fri, 13 Nov 1998 02:34:45 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: Randall Gellens <[email-masked]>
CC: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I sendmailto it?
Sender: [email-masked]

Randall Gellens wrote:

> At 3:13 AM +0300 11/12/98, Alexey Melnikov wrote:
>
> > I am sorry for not being precise. I mean *server implementations* (I am
> > not interested how to configure clients, I want to know if there is any
> > server (MTA-to-MTA) [de-facto] standard)
>
> One way to do this is to have the MX records point to a relay SMTP
> server that listens on port 25, and has been configured to talk to your
> SMTP server on whatever port is likes.  I'm not sure what this buys you
> in the general case, but it might be useful in some limited situations.

Yes, I know that some mail proxy can be used in this way.

--
Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm

Fax (in San Diego, California): 1 (619) 8393837
------------------------------------------

Date: Fri, 13 Nov 1998 02:31:58 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: John C Klensin <[email-masked]>
CC: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
Sender: [email-masked]

John C Klensin wrote:

> On Thu, 12 Nov 1998 03:13:53 +0300 Alexey Melnikov
> <[email-masked]> wrote:
>
> > I am sorry for not being precise. I mean *server implementations* (I am
> > not interested how to configure clients, I want to know if there is any
> > server (MTA-to-MTA) [de-facto] standard)
>
> Short answer: No
>
> There are also multiple reasons why this would be a bad idea.
> They include reintroducing a reason for explicit source routes

Why?

> and a great deal of confusion if the target domain actually
> labels a set of MX records for hosts that don't all use the same
> port.

You are right, this is confusing when we have multiple MX records. I missed
this point when asked the question.

>  If this is "first hop" (e.g., "message submission"), then
> the comments others have made about configuring clients probably
> apply.

Agreed.

>  If it is trying to reach a general far-end system on a
> peculiar port, it probably can't be made to work in the general
> case: the port data would really have to be in the DNS somehow,
> and running standards/well-known services on variant ports is
> usually considered offensive to both the architecture and even
> elementary security considerations.

I am not insisting on using <username>@<server>:<port> syntax.
I would like to know how this idea was implemented (if it was) : server is
specially configured to connect particular server on non standard port (i.e.
the use of configuration files), server uses DNS Well-known service record or
Service Location Protocol, other ways.

--
Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm

Fax (in San Diego, California): 1 (619) 8393837
------------------------------------------

Date: Fri, 13 Nov 1998 02:22:36 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: Randall Gellens <[email-masked]>
CC: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I sendmail to it?
Sender: [email-masked]

Randall Gellens wrote:

> At 1:56 AM +0300 11/12/98, Alexey Melnikov wrote:
>
> > Anybody supports the following trick to send mail to SMTP on different
> > port:
> >
> >  <username>@<host.name.com>:<portnumber>
>
> I'm not sure what specifically you are asking for.  Do you mean you
> want to attach a port number to an email address, so that when the
> message gets through whichever SMTP servers are needed beforehand, and
> is ready to be sent to the final one (the one for the end user), you
> want to instruct the prior SMTP server to use a different port?  That
> is:
>
> You send message to your local SMTP server, it relays to server X, ...
> it sends to final recipient's server, using non-standard port?

Yes. (Suppose I have two SMTP servers on different ports on the same
machine).

> Or do you simply want to instruct your client to use a different port
> when submitting messages?

No, this is too simple :-)

Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm

Fax (in San Diego, California): 1 (619) 8393837
------------------------------------------

Date: Thu, 12 Nov 1998 15:02:40 -0800
To: Alexey Melnikov <[email-masked]>, [email-masked]
From: Randall Gellens <[email-masked]>
Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
Sender: [email-masked]

At 3:13 AM +0300 11/12/98, Alexey Melnikov wrote:

> I am sorry for not being precise. I mean *server implementations* (I am
> not interested how to configure clients, I want to know if there is any
> server (MTA-to-MTA) [de-facto] standard)

One way to do this is to have the MX records point to a relay SMTP 
server that listens on port 25, and has been configured to talk to your 
SMTP server on whatever port is likes.  I'm not sure what this buys you 
in the general case, but it might be useful in some limited situations.

Date: Wed, 11 Nov 1998 23:30:49 -0500 (Eastern Standard Time)
From: John C Klensin <[email-masked]>
Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
To: Alexey Melnikov <[email-masked]>
Cc: [email-masked]
Sender: [email-masked]

On Thu, 12 Nov 1998 03:13:53 +0300 Alexey Melnikov 
<[email-masked]> wrote:

> I am sorry for not being precise. I mean *server implementations* (I am
> not interested how to configure clients, I want to know if there is any
> server (MTA-to-MTA) [de-facto] standard)

Short answer: No

There are also multiple reasons why this would be a bad idea.  
They include reintroducing a reason for explicit source routes 
and a great deal of confusion if the target domain actually 
labels a set of MX records for hosts that don't all use the same 
port.  If this is "first hop" (e.g., "message submission"), then 
the comments others have made about configuring clients probably 
apply.  If it is trying to reach a general far-end system on a 
peculiar port, it probably can't be made to work in the general 
case: the port data would really have to be in the DNS somehow, 
and running standards/well-known services on variant ports is 
usually considered offensive to both the architecture and even 
elementary security considerations.

   john

From: "Norman Widders" <[email-masked]>
Date: Thu, 12 Nov 1998 14:26:07 +1100 (GMT)
Subject: Re: SMTP server resides on non standard port. How can I send mail to it?
To: <[email-masked]>
Organization: Paladin Corporation
Sender: [email-masked]

On Wed, 11 Nov 1998 16:03:43 -0800
Randall Gellens <[email-masked]> scribbled:

Hi,

I believe our friend Alexey means like a URL, where I can specify 

http://www.some.net:70/some.html

.. and some mechanism for parsing the port regardless of client or 
daemon.... ie, [email-masked]:24 from the destination, my thoughts are that 
nobody has probably tried it yet, but it looks interesting imho :)

Cheers

> At 1:56 AM +0300 11/12/98, Alexey Melnikov wrote:
> 
> > Anybody supports the following trick to send mail to SMTP on
> different
> > port:
> >
> >  <username>@<host.name.com>:<portnumber>
> 
> I'm not sure what specifically you are asking for.  Do you mean you 
> want to attach a port number to an email address, so that when the 
> message gets through whichever SMTP servers are needed beforehand,
> and 
> is ready to be sent to the final one (the one for the end user), you
> 
> want to instruct the prior SMTP server to use a different port?  That
> 
> is:
> 
> You send message to your local SMTP server, it relays to server X,
> ... 
> it sends to final recipient's server, using non-standard port?
> 
> Or do you simply want to instruct your client to use a different port
> 
> when submitting messages?
> 
--
----------------------------------------------------------
  Nørman Wïdders   NIC: NW296-AU
  Paladin Corporation Pty Ltd.
  Ph: +612 9835-4782  Fax: +612 9864-0487
----------------------------------------------------------

Date: Wed, 11 Nov 1998 16:03:43 -0800
To: Alexey Melnikov <[email-masked]>, [email-masked]
From: Randall Gellens <[email-masked]>
Subject: Re: SMTP server resides on non standard port. How can I send mail to it?
Sender: [email-masked]

At 1:56 AM +0300 11/12/98, Alexey Melnikov wrote:

> Anybody supports the following trick to send mail to SMTP on different
> port:
>
>  <username>@<host.name.com>:<portnumber>

I'm not sure what specifically you are asking for.  Do you mean you 
want to attach a port number to an email address, so that when the 
message gets through whichever SMTP servers are needed beforehand, and 
is ready to be sent to the final one (the one for the end user), you 
want to instruct the prior SMTP server to use a different port?  That 
is:

You send message to your local SMTP server, it relays to server X, ... 
it sends to final recipient's server, using non-standard port?

Or do you simply want to instruct your client to use a different port 
when submitting messages?

Date: Thu, 12 Nov 1998 03:13:53 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I send mailto it?
Sender: [email-masked]

Dan Wing wrote:

> On Thu, 12 Nov 1998, Alexey Melnikov wrote:
>
> > Hi,
> >
> > I need to set up my SMTP server on non standard port (for whatever
> > reasons).
> > Anybody supports the following trick to send mail to SMTP on different
> > port:
> >
> >  <username>@<host.name.com>:<portnumber>
> >
> > If this question was discussed before, just point me politely :-) to the
> > required information.
>
> There are ways to do this with almost every mailer.
>
> Please ask your question on the "comp.mail.misc" newsgroup.

I am sorry for not being precise. I mean *server implementations* (I am
not interested how to configure clients, I want to know if there is any
server (MTA-to-MTA) [de-facto] standard)

Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm

Fax (in San Diego, California): 1 (619) 8393837
------------------------------------------

Date: Wed, 11 Nov 1998 15:22:43 -0800 (PST)
From: Dan Wing <[email-masked]>
To: Alexey Melnikov <[email-masked]>
cc: [email-masked]
Subject: Re: SMTP server resides on non standard port. How can I send mail to it?
Sender: [email-masked]

On Thu, 12 Nov 1998, Alexey Melnikov wrote:

> Hi,
> 
> I need to set up my SMTP server on non standard port (for whatever
> reasons).
> Anybody supports the following trick to send mail to SMTP on different
> port:
> 
>  <username>@<host.name.com>:<portnumber>
> 
> If this question was discussed before, just point me politely :-) to the
> required information.

There are ways to do this with almost every mailer.

Please ask your question on the "comp.mail.misc" newsgroup.

-Dan Wing

Date: Thu, 12 Nov 1998 01:56:55 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: [email-masked]
Subject: SMTP server resides on non standard port. How can I send mail to it?
Sender: [email-masked]

Hi,

I need to set up my SMTP server on non standard port (for whatever
reasons).
Anybody supports the following trick to send mail to SMTP on different
port:

 <username>@<host.name.com>:<portnumber>

If this question was discussed before, just point me politely :-) to the
required information.

Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm

Fax (in San Diego, California): 1 (619) 8393837
------------------------------------------

Date: Mon, 9 Nov 1998 10:25:10 +0900 (JST)
From: Kenji Rikitake <[email-masked]>
To: [email-masked]
Subject: Re: Proposed change for RFC0974
Sender: [email-masked]

On Fri, 6 Nov 1998, Jack De Winter wrote:
> 1) According to Alexey's reading (and mine) of the rfc, you MUST read
> the first item of a MX record, and MAY go to the other MX records, in
> listed order of preference if a given MX record fails.

I think current SMTP implementation for most MTAs assume that the
recipient MUST be able to handle the SMTP connection requests from the
sender at any time.  So for intermittently-connected sites, the first MX
*MUST* be set to a mail server which is also a continuously-connected
site anyway, for a reliable service.

I understand what Alexey writes, but I think this is rather an
operational issue than a standardization issue, since requiring all MTAs
to poll all MX sites sounds quite inpractical to me.  Maybe the
"stronger wording to suggest" Jack mentioned is one of few things we can
do for revising the standard document.

// Kenji Rikitake

Date: Sun, 08 Nov 1998 22:52:39 +0100
To: Jack De Winter <[email-masked]>, [email-masked], "Norman Widders" <[email-masked]>
From: Harald Tveit Alvestrand <[email-masked]>
Subject: Re: Proposed change for RFC0974
Cc: [email-masked], [email-masked]
Sender: [email-masked]

At 10:56 06.11.98 -0500, Jack De Winter wrote:
>3) DJB feels that having a [static] A record for a site that is only ever
>intermittantly connected is a waste.  [For the record, I think this is a
>bit silly too.  Using DHCP from a dynamic pool would be better if a
>proper solution such as ETRN or ATRN is provided.]

I've run with this solution for an interminenttly-connected PC for
a few years (static IP on office LAN, laptop that went with me on trips).

Sometimes its name escaped into the Great Wild Yonder, so people would
send mail to it, so I had an MX (the lowest-valued one, in fact) pointing
to my "spool" mailhost. (You can still find it in Four11, I think).

If I had trusted my mail+news+other mailers not to reveal the hostname,
I might not have bothered with the MX, and thus have been one of the
Bad Boys with a working mail system on an interminenttly-connected host.

But the A record was, I think, better present than absent; it was
always telling the truth about the connection between the name and the
IP address, just not saying anything about whether it was there or not.

                      Harald A

-- 
Harald Tveit Alvestrand, Maxware, Norway
[email-masked]

Date: Fri, 06 Nov 1998 10:56:07 -0500
To: [email-masked], "Norman Widders" <[email-masked]>
From: Jack De Winter <[email-masked]>
Subject: Re: Proposed change for RFC0974
Cc: [email-masked], [email-masked]
Sender: [email-masked]

At 10:02 AM 11/6/98 -0500, [email-masked] wrote:
>On Fri, 06 Nov 1998 22:18:45 +1100, you said:
>Now, it just so happens that many of these offending sites don't HAVE
>MX entries, so we attempt delivery to their A record.  I think the point
>that was being made was that if they *had* MX entries with a backup at
>their ISP, that they couldn't use ETRN to suck down their mail unless my
>machine properly handled rollover to the backup MX entry, because their
>machine wouldn't know to ETRN to mine, only to the ISP's server.
>
>Are there, in fact, any systems with significant market share that manage
>to get MX record handling wrong?

My take on this was entirely different.  I think the points being raised
are:

1) According to Alexey's reading (and mine) of the rfc, you MUST read
the first item of a MX record, and MAY go to the other MX records, in
listed order of preference if a given MX record fails.

2) There are quite a few sites out there that have an A record and no
MX record.

3) DJB feels that having a [static] A record for a site that is only ever
intermittantly connected is a waste.  [For the record, I think this is a
bit silly too.  Using DHCP from a dynamic pool would be better if a
proper solution such as ETRN or ATRN is provided.]

>From my POV, if you have a list of 500 people, and 5% of those addresses
are hosts that have tenuous connections to the net, that means for 25
connections, you will try and connect to the first MX record or A record.  
In the standard case for both, you will fail the connection.  For the
MX record case, you may decide to go to MX record #2, which if it is the
ISP, has a far better chance of being reachable.

So, my take on this entire thing is that Alexey thinks it would be a real
good idea if we did something about this.  The A record case is one that
we really can't do anything more about than hand-slapping ("you should
really set up MX records for your mail server!").  For the MX record case,
perhaps all Alexey is asking for is stronger wording to suggest:

that if a given host will normally not be connected to the net that it
not appear in the MX records, but have a method for contacting the node
listed as the "most preferable" host by MX record, and getting the mail
sent from there.

ideas?

regards,
Jack
-------------------------------------------------
Jack De Winter - Wildbear Consulting, Inc.
(519) 884-4498		http://www.wildbear.on.ca/homepages/jack/

To: [email-masked]
Cc: "Norman Widders" <[email-masked]>, [email-masked]
Subject: Re: Proposed change for RFC0974
From: Arnt Gulbrandsen <[email-masked]>
Date: 06 Nov 1998 16:25:23 +0100
Lines: 11
Sender: [email-masked]

[email-masked]
> Are there, in fact, any systems with significant market share that manage
> to get MX record handling wrong?

What has significant market share, except sendmail and perhaps
exchange?  Whatever firewall says this behaved badly yesterday,
market share or not:

    220 CheckPoint FireWall-1 secure SMTP server

--Arnt

To: "Norman Widders" <[email-masked]>
Cc: [email-masked]
Subject: Re: Proposed change for RFC0974 
From: [email-masked]
Date: Fri, 06 Nov 1998 10:02:19 -0500
Sender: [email-masked]

--==_Exmh_1194623522P
Content-Type: text/plain; charset=us-ascii

On Fri, 06 Nov 1998 22:18:45 +1100, you said:
> Forgive the question, but whats the difference between an IP that is down 
> because of lets say Scheduled Network-Maintenance _and_ an offline host ?
> Perhaps I am wrong but to all intents they appear the same, yes ?

Well, for *one* delivery, they appear the same.  The distinction is on
the long-term differences.  The machine I'm posting this from handles a
fair amount of mail per day (500+ items a day or more).  Now, if one
recipient host does down for a backup for 30 minutes, my machine will just
re-queue and re-try later.  However, many machines I send mail to are
*chronically* unavailable (to the point where a retry-every-30-mins
strategy still times out after 5 days).

Now, it just so happens that many of these offending sites don't HAVE
MX entries, so we attempt delivery to their A record.  I think the point
that was being made was that if they *had* MX entries with a backup at
their ISP, that they couldn't use ETRN to suck down their mail unless my
machine properly handled rollover to the backup MX entry, because their
machine wouldn't know to ETRN to mine, only to the ISP's server.

Are there, in fact, any systems with significant market share that manage
to get MX record handling wrong?

-- 
				Valdis Kletnieks
				Computer Systems Senior Engineer
				Virginia Tech

--==_Exmh_1194623522P
Content-Type: application/pgp-signature

--==_Exmh_1194623522P--

From: "Norman Widders" <[email-masked]>
Date: Fri, 6 Nov 1998 22:18:45 +1100 (GMT)
Subject: Re: Proposed change for RFC0974
To: <[email-masked]>
Organization: Paladin Corporation
Sender: [email-masked]

On 6 Nov 1998 00:27:50 -0000
"D. J. Bernstein" <[email-masked]> scribbled:

Forgive the question, but whats the difference between an IP that is down 
because of lets say Scheduled Network-Maintenance _and_ an offline host ?
Perhaps I am wrong but to all intents they appear the same, yes ?

yours faithfully, Norman Widders

> Albert Louw writes:
> > Although it's very easy to say that a 'off-line' mailhost should
> not
> > have an MX record,
> 
> Indeed. It's rude to put an IP address into a global DNS record if
> the
> address isn't globally reachable. You're wasting valuable client
> time
> that could have been used for successful deliveries to other hosts.
> 
> Most MTAs, under most circumstances, will try at least two MX
> records,
> but if you're relying on this then you should fix your
> configuration.
--
----------------------------------------------------------
  Nørman Wïdders   NIC: NW296-AU
  Paladin Corporation Pty Ltd.
  Ph: +612 9835-4782  Fax: +612 9864-0487
----------------------------------------------------------

Date: Fri, 06 Nov 1998 01:35:37 +0100
From: "Albert Louw" <[email-masked]>
To: <[email-masked]>
Cc: <[email-masked]>
Subject: Re: Proposed change for RFC0974
Sender: [email-masked]

That's the point yes.

---
Albert Louw
Research & Development Dept.
Azlan Network Services

>>> Alexey Melnikov <[email-masked]> 11/06 1:11 AM >>>
"Doug Strauss (Exchange)" wrote:

> There are other conditions to think about with this logic.
>         1.  The host which has the mail queued for delivery is obviously in
> the MX list.
>         2.  Delivery to MX records should exclude all MX records of equal or
> greater values.
>
> Thus if the config is correct, you would only be trying to deliver to the
> lowest MX record which is either closer to the final host or is the static
> IP of the final destination.
>
> Assuming you are following this it should solve the problem you state does
> it not?

I think Albert mentioned different problem:

If the attempt to deliver mail to the host with lowest MX value will fail,
client MUST (Albert propose), instead of MAY (current wording) try to send mail
to the host with higher MX value. But the host with the lowest MX is batched
host, that is down most of the time. The problem is that many implementations
just ignore MAY and mail is undelivered.

> -doug
> Microsoft Exchange SMTP test lead
>
> -----Original Message-----
> From: Albert Louw [mailto:[email-masked]] 
> Sent: Thursday, November 05, 1998 1:19 PM
> To: [email-masked] 
> Subject: Proposed change for RFC0974
>
> Hi,
>
> After checking into some heavy problems with some commercial SMTP mailers
> and SMTP proxy servers it was time to check on the standards and I found
> that there's quite a problem there.
> The world is filling up with mail servers that are only available thru
> batched smtp (waiting to be released by the ETRN command in SMTP (rfc1985).
> Looking at the below part of RFC0974 (last paragraph of page 5, inserted
> below to make sure we're reading the same) a mailer MUST try the preference
> with the lowest value (in 9916433467503f the batched SMTP cases the actual
> host behind the dial-up link) and MAY try to go on to higher valued
> preferences if the first attempt fails.
>
> Since an average batched host link is down most of the time, the message is
> almost doomed to be undeliverable, if a mailer only implements the 'MUST'
> features. Although it's very easy to say that a 'off-line' mailhost should
> not have an MX record, it's still the reality today and with many ISPs their
> standard way of creating batched smtp.
>
> So, in conclusion, I'd propose a change for the part that a server MAY try
> the second host in line to MUST try at least the second host in line to
> ensure that all batched SMTP mail is delivered.
>
> Looking forward to your comment,
>
> ********* start quote **********
> If the list of MX RRs is not empty, the mailer should try to deliver the
> message to the MXs in order (lowest preference value tried first). The
> mailer is required
>      to attempt delivery to the lowest valued MX. Implementors are
> encouraged to write mailers so that they try the MXs in order until one of
> the MXs accepts the
>      message, or all the MXs have been tried. A somewhat less demanding
> system, in which a fixed number of MXs is tried, is also reasonable. Note
> that multiple
>      MXs may have the same preference value. In this case, all MXs at with a
> given value must be tried before any of a higher value are tried. In
> addition, in the
>      special case in which there are several MXs with the lowest preference
> value, all of them should be tried before a message is deemed undeliverable.
>
> ********** end quote ***********
>
> ---
> Albert Louw
> Research & Development Dept.
> Azlan Network Services
>
> ---
> SkyNet MailServer v1.00Beta
> Copyright 1998 A.J. Louw. All Rights Reserved.

Best Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team
"ACAP Explorer" client

Epsylon Technologies, Russia
 http://www.taxxi.com 

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm 
------------------------------------------

---
SkyNet MailServer v1.00Beta
Copyright 1998 A.J. Louw. All Rights Reserved.

---
SkyNet MailServer v1.00Beta
Copyright 1998 A.J. Louw. All Rights Reserved.

Date: 6 Nov 1998 00:27:50 -0000
Mail-Followup-To: [email-masked]
From: "D. J. Bernstein" <[email-masked]>
To: [email-masked]
Subject: Re: Proposed change for RFC0974
Sender: [email-masked]

Albert Louw writes:
> Although it's very easy to say that a 'off-line' mailhost should not
> have an MX record,

Indeed. It's rude to put an IP address into a global DNS record if the
address isn't globally reachable. You're wasting valuable client time
that could have been used for successful deliveries to other hosts.

Most MTAs, under most circumstances, will try at least two MX records,
but if you're relying on this then you should fix your configuration.

---Dan
1000 recipients, 28.8 modem, 10 seconds. http://pobox.com/~djb/qmail/mini.html

Date: Fri, 06 Nov 1998 03:11:16 +0300
From: Alexey Melnikov <[email-masked]>
Organization: Epsylon Technologies
To: "Doug Strauss (Exchange)" <[email-masked]>
CC: "'Albert Louw'" <[email-masked]>, [email-masked]
Subject: Re: Proposed change for RFC0974
Sender: [email-masked]

"Doug Strauss (Exchange)" wrote:

> There are other conditions to think about with this logic.
>         1.  The host which has the mail queued for delivery is obviously in
> the MX list.
>         2.  Delivery to MX records should exclude all MX records of equal or
> greater values.
>
> Thus if the config is correct, you would only be trying to deliver to the
> lowest MX record which is either closer to the final host or is the static
> IP of the final destination.
>
> Assuming you are following this it should solve the problem you state does
> it not?

I think Albert mentioned different problem:

If the attempt to deliver mail to the host with lowest MX value will fail,
client MUST (Albert propose), instead of MAY (current wording) try to send mail
to the host with higher MX value. But the host with the lowest MX is batched
host, that is down most of the time. The problem is that many implementations
just ignore MAY and mail is undelivered.

> -doug
> Microsoft Exchange SMTP test lead
>
> -----Original Message-----
> From: Albert Louw [mailto:[email-masked]]
> Sent: Thursday, November 05, 1998 1:19 PM
> To: [email-masked]
> Subject: Proposed change for RFC0974
>
> Hi,
>
> After checking into some heavy problems with some commercial SMTP mailers
> and SMTP proxy servers it was time to check on the standards and I found
> that there's quite a problem there.
> The world is filling up with mail servers that are only available thru
> batched smtp (waiting to be released by the ETRN command in SMTP (rfc1985).
> Looking at the below part of RFC0974 (last paragraph of page 5, inserted
> below to make sure we're reading the same) a mailer MUST try the preference
> with the lowest value (in 9916433467503f the batched SMTP cases the actual
> host behind the dial-up link) and MAY try to go on to higher valued
> preferences if the first attempt fails.
>
> Since an average batched host link is down most of the time, the message is
> almost doomed to be undeliverable, if a mailer only implements the 'MUST'
> features. Although it's very easy to say that a 'off-line' mailhost should
> not have an MX record, it's still the reality today and with many ISPs their
> standard way of creating batched smtp.
>
> So, in conclusion, I'd propose a change for the part that a server MAY try
> the second host in line to MUST try at least the second host in line to
> ensure that all batched SMTP mail is delivered.
>
> Looking forward to your comment,
>
> ********* start quote **********
> If the list of MX RRs is not empty, the mailer should try to deliver the
> message to the MXs in order (lowest preference value tried first). The
> mailer is required
>      to attempt delivery to the lowest valued MX. Implementors are
> encouraged to write mailers so that they try the MXs in order until one of
> the MXs accepts the
>      message, or all the MXs have been tried. A somewhat less demanding
> system, in which a fixed number of MXs is tried, is also reasonable. Note
> that multiple
>      MXs may have the same preference value. In this case, all MXs at with a
> given value must be tried before any of a higher value are tried. In
> addition, in the
>      special case in which there are several MXs with the lowest preference
> value, all of them should be tried before a message is deemed undeliverable.
>
> ********** end quote ***********
>
> ---
> Albert Louw
> Research & Development Dept.
> Azlan Network Services
>
> ---
> SkyNet MailServer v1.00Beta
> Copyright 1998 A.J. Louw. All Rights Reserved.

Best Regards,
Alexey Melnikov
------------------------------------------
SMTP/POP3/IMAP4/ACAP servers creation team
"ACAP Explorer" client

Epsylon Technologies, Russia
 http://www.taxxi.com

Imap Development Kit (my own product)
http://194.87.43.111/homerus/mail/idk/index.htm
------------------------------------------

Date: Thu, 5 Nov 1998 15:48:41 -0800
To: "Doug Strauss (Exchange)" <[email-masked]>, "'Albert Louw'" <[email-masked]>, [email-masked]
From: Randall Gellens <[email-masked]>
Subject: RE: Proposed change for RFC0974
Sender: [email-masked]

At 1:57 PM -0800 11/5/98, Doug Strauss (Exchange) wrote:

> There are other conditions to think about with this logic.
> 	1.  The host which has the mail queued for delivery is obviously in
> the MX list.
> 	2.  Delivery to MX records should exclude all MX records of equal or
> greater values.
>
> Thus if the config is correct, you would only be trying to deliver to the
> lowest MX record which is either closer to the final host or is the static
> IP of the final destination.
>
> Assuming you are following this it should solve the problem you state does
> it not?

My understanding of Albert's message is this:

1.  A number of domains are set up with their own, 
intermittently-connected mail server as the lowest-preference MX, and 
their ISP (with a full-time connection) as the next MX.

2.  Random sites trying to send mail might use an SMTP server which, in 
compliance with the MUST of 974, only attempts to contact the 
lowest-preference MX, which is not likely to be connected.

Note that 821bis, in "5. Address Resolution and Mail Handling" says:

> To provide reliable mail transmission, the
> SMTP client MUST be able to try (and retry) each of the relevant addresses
> in this list in order, until a delivery attempt succeeds. However, there
> MAY also be a configurable limit on the number of alternate addresses that
> can be tried.  In any case, a host SHOULD try at least two addresses.

Which I think addresses Albert's concern.

From: "Doug Strauss (Exchange)" <[email-masked]>
To: "'Albert Louw'" <[email-masked]>, [email-masked]
Subject: RE: Proposed change for RFC0974
Date: Thu, 5 Nov 1998 13:57:05 -0800 
Sender: [email-masked]

There are other conditions to think about with this logic.
	1.  The host which has the mail queued for delivery is obviously in
the MX list.
	2.  Delivery to MX records should exclude all MX records of equal or
greater values.

Thus if the config is correct, you would only be trying to deliver to the
lowest MX record which is either closer to the final host or is the static
IP of the final destination.

Assuming you are following this it should solve the problem you state does
it not?

-doug
Microsoft Exchange SMTP test lead

-----Original Message-----
From: Albert Louw [mailto:[email-masked]]
Sent: Thursday, November 05, 1998 1:19 PM
To: [email-masked]
Subject: Proposed change for RFC0974

Hi,

After checking into some heavy problems with some commercial SMTP mailers
and SMTP proxy servers it was time to check on the standards and I found
that there's quite a problem there. 
The world is filling up with mail servers that are only available thru
batched smtp (waiting to be released by the ETRN command in SMTP (rfc1985).
Looking at the below part of RFC0974 (last paragraph of page 5, inserted
below to make sure we're reading the same) a mailer MUST try the preference
with the lowest value (in 9916433467503f the batched SMTP cases the actual
host behind the dial-up link) and MAY try to go on to higher valued
preferences if the first attempt fails. 

Since an average batched host link is down most of the time, the message is
almost doomed to be undeliverable, if a mailer only implements the 'MUST'
features. Although it's very easy to say that a 'off-line' mailhost should
not have an MX record, it's still the reality today and with many ISPs their
standard way of creating batched smtp.

So, in conclusion, I'd propose a change for the part that a server MAY try
the second host in line to MUST try at least the second host in line to
ensure that all batched SMTP mail is delivered.

Looking forward to your comment,

********* start quote **********
If the list of MX RRs is not empty, the mailer should try to deliver the
message to the MXs in order (lowest preference value tried first). The
mailer is required
     to attempt delivery to the lowest valued MX. Implementors are
encouraged to write mailers so that they try the MXs in order until one of
the MXs accepts the
     message, or all the MXs have been tried. A somewhat less demanding
system, in which a fixed number of MXs is tried, is also reasonable. Note
that multiple
     MXs may have the same preference value. In this case, all MXs at with a
given value must be tried before any of a higher value are tried. In
addition, in the
     special case in which there are several MXs with the lowest preference
value, all of them should be tried before a message is deemed undeliverable.

********** end quote ***********

---
Albert Louw
Research & Development Dept.
Azlan Network Services

---
SkyNet MailServer v1.00Beta
Copyright 1998 A.J. Louw. All Rights Reserved.

Date: Thu, 05 Nov 1998 22:18:59 +0100
From: "Albert Louw" <[email-masked]>
To: <[email-masked]>
Subject: Proposed change for RFC0974
Sender: [email-masked]

Hi,

After checking into some heavy problems with some commercial SMTP mailers and SMTP proxy servers it was time to check on the standards and I found that there's quite a problem there. 
The world is filling up with mail servers that are only available thru batched smtp (waiting to be released by the ETRN command in SMTP (rfc1985). Looking at the below part of RFC0974 (last paragraph of page 5, inserted below to make sure we're reading the same) a mailer MUST try the preference with the lowest value (in 9916433467503f the batched SMTP cases the actual host behind the dial-up link) and MAY try to go on to higher valued preferences if the first attempt fails. 

Since an average batched host link is down most of the time, the message is almost doomed to be undeliverable, if a mailer only implements the 'MUST' features. Although it's very easy to say that a 'off-line' mailhost should not have an MX record, it's still the reality today and with many ISPs their standard way of creating batched smtp.

So, in conclusion, I'd propose a change for the part that a server MAY try the second host in line to MUST try at least the second host in line to ensure that all batched SMTP mail is delivered.

Looking forward to your comment,

********* start quote **********
If the list of MX RRs is not empty, the mailer should try to deliver the message to the MXs in order (lowest preference value tried first). The mailer is required
     to attempt delivery to the lowest valued MX. Implementors are encouraged to write mailers so that they try the MXs in order until one of the MXs accepts the
     message, or all the MXs have been tried. A somewhat less demanding system, in which a fixed number of MXs is tried, is also reasonable. Note that multiple
     MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried. In addition, in the
     special case in which there are several MXs with the lowest preference value, all of them should be tried before a message is deemed undeliverable. 
********** end quote ***********

---
Albert Louw
Research & Development Dept.
Azlan Network Services

---
SkyNet MailServer v1.00Beta
Copyright 1998 A.J. Louw. All Rights Reserved.