[EAI] MTA -> Final delievery MTA -> MDA (Re: MIME questions)

[Kari Hurtta <hurtta+gmane at siilo.fmi.fi>]

Frank Ellermann <nobody at xyzzy.claranet.de> writes
on gmane.ietf.ima:

> Charles Lindsey wrote:
> 
> > If the MIME structure of broken, then Garbage-in
> > Garbage-out. That is already true with out UTF8SMTP.
> 
> Kari's proposal would bounce anything misidentified
> as message/utf-8 at the final delivery MTA, if the
> LMTP-MDA says "no, thanks, legacy mailbox".  That's
> not GiGo, it's more like "garbage in, garbage back".

Lets look one possibility when downgrade fails.

        C   is SMTP clent
        F   is is final delivery MTA
        D   is MDA

C -> F      is SMTP
F -> D      is LMTP

         Lets assume that there is two new SMTP reply codes (used
             after final dot)

         ABC             Some recipeints do not support UTF8SMTP,
                         downgrade failed, retry with one RCPT TO
                         on transaction

         XYZ             All recipeints do not support, downgrade failed

         XYZ             LMTP:  This recipeint does not support
                                 UTF8SMTP, downgrade failed




C -> F             [ Smtp clients open connection ]
C <- F             220 mail.example.com ready
C -> F             EHLO mail.example.org
C <- F             250-mail.example.com
C <- F             250-8BITMIME
C <- F             250-SIZE
C <- F             250 UTF8SMTP
C -> F             MAIL FROM:<support at example.org> BODY=7BIT SIZE=323
C <- F             250 Ok.
C -> F             RCPT TO:<client at example.com>
C <- F             250 Ok.
C -> F             RCPT TO:<boss at example.com>
C <- F             250 Ok.
C -> F             DATA
C <- F             354 Start mail input; end with <CRLF>.<CRLF>
C -> F             Received: by mail.example.org with UTF8SMTP
C -> F               id JGR17356;
C -> F               Wed, 13 Sep 2007 22:27:25 +0300
C -> F             From: <KÃyttÃjÃtuki at example.org>
C -> F             To: <client at example.com>
C -> F             Subject: [#XCVXBX] NÃppÃimistà rikki
C -> F             Message-ID: <8YmZIwmbXHwhvo4Cksf at example.org>
C -> F             Mime-Version: 1.0
C -> F             Content-Type: text/plain
C -> F
C -> F             Your case #XCVXBX is closed.
C -> F             .                  
     F -> D        [ final delivery MTA opens connection to MDA ]
     F <- D        220 mail.example.com ready
     F -> D        LHLO mail.example.com
     F <- D        250-mail.example.com       
     F <- D        250-8BITMIME
     F <- D        250-SIZE
     F <- D        250 UTF8SMTP
     F -> D        MAIL FROM:<support at example.org> BODY=7BIT SIZE=437
     F <- D        250 Ok.
     F -> D        RCPT TO:<client at example.com>
     F <- D        250 Ok.
     F -> D        RCPT TO:<boss at example.com>
     F <- D        250 Ok.
     F -> D        DATA
     F <- D        354 Start mail input; end with <CRLF>.<CRLF>
     F -> D        Received: from mail.example.org by mail.example.com with UTF8SMTP
     F -> D         id dfsdafsdf;
     F -> D         Wed, 13 Sep 2007 22:27:26 +0300
     F -> D        Received: by mail.example.org with UTF8SMTP
     F -> D          id JGR17356;
     F -> D          Wed, 13 Sep 2007 22:27:25 +0300
     F -> D        From: <KÃyttÃjÃtuki at example.org>
     F -> D        To: <client at example.com>
     F -> D        Subject: [#XCVXBX] NÃppÃimistà rikki
     F -> D        Message-ID: <8YmZIwmbXHwhvo4Cksf at example.org>
     F -> D        Mime-Version: 1.0
     F -> D        Content-Type: text/plain
     F -> D
     F -> D        Your case #XCVXBX is closed.
     F -> D        .                  
     F <- D        250 Message parsed, UTF8SMTP detected
     F <- D        250 <client at example.com> sttored
     F <- D        XYZ <boss at example.com> UTF8SMTP not accepted

     [ final delivery MTA adds triple
        (support at example.org,client at example.com,8YmZIwmbXHwhvo4Cksf at example.org) = delivered
       to database

       final delivery MTA tries downgrade message, but fails

       final delivery MTA adds triple
        (support at example.org,boss at example.com,8YmZIwmbXHwhvo4Cksf at example.org) = downgrade failure
       to database
     ]

     F -> D        QUIT
     F <- D        221 mail.example.com closing connection

C <- F             ABC UTf8SMTP downgrade fails for some recipients
C -> F             MAIL FROM:<support at example.org> BODY=7BIT SIZE=323
C <- F             250 Ok.
C -> F             RCPT TO:<client at example.com>
C <- F             250 Ok.
C <- F             354 Start mail input; end with <CRLF>.<CRLF>
C -> F             Received: by mail.example.org with UTF8SMTP
C -> F               id JGR17356;
C -> F               Wed, 13 Sep 2007 22:27:25 +0300
C -> F             From: <KÃyttÃjÃtuki at example.org>
C -> F             To: <client at example.com>
C -> F             Subject: [#XCVXBX] NÃppÃimistà rikki
C -> F             Message-ID: <8YmZIwmbXHwhvo4Cksf at example.org>
C -> F             Mime-Version: 1.0
C -> F             Content-Type: text/plain
C -> F
C -> F             Your case #XCVXBX is closed.
C -> F             .                  
C <- F             250 Message already delivered
C -> F             MAIL FROM:<support at example.org> BODY=7BIT SIZE=323
C <- F             250 Ok.
C -> F             RCPT TO:<boss at example.com>
C <- F             250 Ok.
C -> F             DATA
C <- F             354 Start mail input; end with <CRLF>.<CRLF>
C -> F             Received: by mail.example.org with UTF8SMTP
C -> F               id JGR17356;
C -> F               Wed, 13 Sep 2007 22:27:25 +0300
C -> F             From: <KÃyttÃjÃtuki at example.org>
C -> F             To: <client at example.com>
C -> F             Subject: [#XCVXBX] NÃppÃimistà rikki
C -> F             Message-ID: <8YmZIwmbXHwhvo4Cksf at example.org>
C -> F             Mime-Version: 1.0
C -> F             Content-Type: text/plain
C -> F
C -> F             Your case #XCVXBX is closed.
C -> F             .                  
C <- F             XYZ UTF8SMTP downgrade fails
C -> F             QUIT
C <- F             221 mail.example.com closing connection


In that example it was assumed that there is MIME parser
on MDA. That is very unlikely.  So actually it is very
usefull that there is HDR=UTF8SMTP parameter on LMTP
MAIL FROM. 

/ Kari Hurtta


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