[EAI] Re: draft-hurtta-eai-messagestore-00.txt

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

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

> | If communication between final delivery MTA and MDA use
> | LMTP, UTF8SMTP response to LHLO command tells that MDA
> | is UTF8SMTP
> 
> That's rather late to decide this.  Is your model limited
> to verified (SPF PASS or similar) return paths ?  It won't
> fly if you drop undeliverable message/utf-8 at the final
> delivery MTA.

That was on part of "Notes:" items. Previous item was:

|   o  If final delivery MTA is UTF8SMTP aware, it is recommended that
|      MDA is arranged that way that it is UTF8SMTP aware.

You was taking it out from context.



Yes, if next hop (this time it is MDA) is not UTF8SMTP aware
there is following possibilities on final MTA:

        - MTA rejects final dot on DATA on SMTP level, if there is 
          at least one RCPT TO which was local
          and MTA discovers that message is UTF8SMTP (by parsing it).
        - MTA downgrades message if there is 
          at least was at least one RCPT TO which was local
          and MTA discovers that message is UTF8SMTP (by parsing it).
        - MTA sends undeliverable DSN for local recipients
          when  MTA discovers that message is UTF8SMTP (by parsing it).

If HDR=UTF8SMTP parameter is added protocol, then there is 
also following possibility on table:

       - MTA rejects RCPT TO command which was local if
         HDR=UTF8SMTP parameter was given on MAIL FROm -command.




Actually it is often late in also when final MTA rejects message
on SMTP level.  Usually picture is:

                             +-------------+                +-------------+
                             |  "border"   |                |    final    |
 Internet     -----ESMTP---> |    MTA      |  --- ESMTP---> |     MTA     |
                             |             |                |             |
                             +-------------+                +-------------+


Anything what was rejected by final MTA tend to cause backscatter
on case of junk mail with forged return path. Often that is full mailbox.
That information is quite difficult to transfer to "border" MTA.
( On general case you even do not know is mailbox "full" before
  you are seen final dot after DATA -- before that you do not really
  know size of mail.)

/ Kari Hurtta


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