Re: Operations requirement: no hop-by-hop

At 9:32 AM +0100 2/16/04, Iljitsch van Beijnum wrote:
>>If your requirement is that there be full authentication before 
>>communication, fine. My requirement is that I can communicate with 
>>people who I cannot authenticate ahead of time.
>
>Full authentication doesn't necessarily follow here. A simple return 
>routability check would also go a long way.

In today's spam environment, that is possibly true. But if we could 
magically turn on full routability in SMTP, spammers would adjust 
their tactics. They have done so for every block we have put in their 
path.

We are trying to design a *next-generation* protocol, not a temporary 
patch. It is not useful to say "I have a requirement that spammers 
will probably get around after I implement it."

>I'm thinking about a layered policy mechanism that would work 
>something like this:
>
>- apply personal white list
>- apply system-wide blacklist
>- apply personal blacklist
>- allow all strongly authenticatable sources (ie others who can 
>present a certificate that we can authenticate directly or using a 
>trusted CA)
>- reject everything that looks too much like spam
>- reject/defer attachments that are too big
>- allow everything else if the return address works

If those are your requirements, then we are in agreement. All of that 
works fine without policy in the middle of the transmission stream.

>In a setup like this the MTA would need to know personal white and 
>black lists, spamcheck yes/no and attachment limits for 
>known/unknown sources.

By "the MTA", you mean *your* MTA. No problem there. There is still 
no policy in the transmission stream. You can instruct your MTA what 
to accept and what to reject without policy being enforced in the 
transmission stream.

Please explain how you requirements above requires your MTA to tell 
the sending MTA (or the sender, if the eventual protocol has no 
initiating MTA) what the policies are ahead of time. Why can that not 
be done at the time of message delivery, after the message's metadata 
has been passed?

--Paul Hoffman, Director
--Internet Mail Consortium