Re: [ietf-smtp] Endless debate on IP literals

[Keith Moore <[e-mail]>]

On 1/1/20 1:38 PM, John Levine wrote:

> In article<[e-mail]>  you write:
>> I've been wondering if there's a need to talk about (for lack of a
>> better term) "pre-submission relaying" which happens when a message is
>> (for whatever reason) not initially submitted to a real submission
>> server that does whatever sanity checking and fixup are needed to make
>> the message suitable for relaying into the global email system.
> I don't see any need to tie ourselves into knots about this.  If you
> want multiple submission hops before the real submission server, you
> don't need to do anything special beyond ensuring that at each hop,
> the server end has some way to limit who's relaying through it.  It
> might be by IP range, or client authentication, or any of a variety of
> other hacks invented over the years.  (POP-before-Submit, known in the
> old days as POP-before-SMTP, comes to mind.)
>
> My DMA submission servers do submision relay.  It works fine.

I agree that this isn't rocket science for anyone who really understands 
email, knows how to configure MTAs, and controls the entire signal path 
up to the submission server.    I also believe that most existing MTAs 
are perfectly capable of being configured to properly play any of these 
roles.

In my mind the question is: how to explain to ordinary operators, 
administrators, IoT device vendors, etc. how to make this work well?    
If someone is developing an IoT device that needs to send mail, what is 
that device required to do, what configuration options should it offer, 
etc.?   If an IT person in some enterprise is arranging for that 
enterprise's IoT devices to be able to send mail, what service do they 
need to provide, on what port, etc?   Does a submission service that's 
in the signal path for outgoing mail for such devices need any special 
configuration or considerations to be able to handle such mail?   (For 
example, does it need to be able to rewrite sender addresses containing 
IP address literals to make them globally meaningful while still being 
distinct from one another for different sender hosts?)   If the operator 
of the IoT devices can say to the enterprise IT person - I need an 
instance of service X, as defined by RFCYYYY, that might make things 
easier and reduce the amount of gratuitous meddling that people do with 
email.   Similarly if the developer of the IoT device knows exactly what 
the messages should look like and what service to interface to, that 
might make configuration of such devices either and reduce the chance 
that special measures will be needed for that device's email.

But I also have seen occasions on which even experts trying to do the 
right things, disagreed about how to do those things, in ways that 
caused problems when their systems interacted.   So I'm not sure that 
the standards are only for "ordinary" operators, etc.

Keith

p.s. I somehow doubt that we should recommend authentication based only 
on IP address at any level, though.    That's poor practice even for a 
small network that assigns static IP addresses to all of its hosts.   
More broadly there's a widespread misconception that isolated networks 
are not subject to security threats or that perimeter defenses are 
sufficient to protect them, even when such networks are used to manage 
critical infrastructure or equipment that can create hazards if not 
properly managed.