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Re: [ietf-smtp] Characteristics of Isolated (or mostly-isolated) industrial IP Networks

2020-01-06 08:13:51

On 1/5/2020 2:38 AM, Keith Moore wrote:
On 1/5/20 12:58 AM, Dave Crocker wrote:

I suspect ietf-smtp would do better to define the behavior of a
submission service that is designed to accept inbound email from
devices in such an environment

The clients in such an environment appear to simply be MUAs.  The
submission server appears simply to be an MSA.

The clients might have MTA-like functions like queuing and retry, but
aren't likely to bounce mail.   From the outside they look a lot like

Hi Keith,

You certainly touched base and highlighted the fact there are both legacy and current forms of small footprint and specialized SMTP transport clients.

I have a number of these. One is a proprietary server/client that works over a virtual dialup/socket system. Its for our GUI frontend "wcNavigator" app that includes a Mail Reader/Writer component (MUA). The connection and thus, its MTA is always authenticated so the backend hosting SMTP would be an MSA per se. The backend is a GUI server that contains a smtp server for the gui smtp clients that can be a mail client or a game client sending notifications.

The mail client can send reply, forwarded, new messages via an API or the backend hosting SMTP server. When the SMTP method is enabled, one mail client uses HELO with no field data and the game client uses HELO with the user's name (No verification necessary). They also use other proprietary SMTP commands and attributes that the server recognizes such as:

MAIL CONF:<conf number> [FORWARD:<conf number>;<message id>]
RCPT CC:<receiver-path>
ATCH NAME:<filename> SIZE:<filesize>

But this is within a closed proprietary boundary environment. The GUI MUA/MTA is not going to connect to a general SMTP server.

In my opinion, RFC5321bis should be about the public service port where we have unsolicited, anonymous senders and we are basically trying to clarify what can be commonly done to strengthen SMTP compliancy or maybe perhaps relax it.



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