Date: Fri, 14 Jul 2000 14:59:50 +0100 (BST)
From: Philip Hazel <ph10@cus.cam.ac.uk>
To: Dave Sill <de5-drums@sws5.ctd.ornl.gov>
cc: drums@cs.utk.edu
Subject: Re: Message munging?
In-Reply-To: <14703.5836.586133.146450@sws5.ctd.ornl.gov>
Message-ID: <Pine.SOL.4.21.0007141455010.29698-100000@draco.cus.cam.ac.uk>
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On Fri, 14 Jul 2000, Dave Sill wrote:

> I understand that 821 only covers message transfer between hosts, and
> that hosts can do what they want once the message is received, but
> does it not provide any guarantee that a message leaving one host
> bears a resemblence to the message received by another? So if
> Microsoft Exchange replaced all occurrences of the string "Winblows"
> with "Windows"--even for messages it's only relaying--that wouldn't
> violate any RFC's? Strange.

Ah well, that depends on what you mean by "relaying". The new draft for 
821bis says:

  2.3.8 Originator, Delivery, Relay, and Gateway Systems            
                                                              
  This specification makes a distinction among four types of SMTP            
  systems, based on the role those systems play in transmitting             
  electronic mail.  An "originating" system (sometimes called an SMTP   
  originator) introduces mail into the Internet or, more generally, into  
  a transport service environment.  A "delivery" SMTP system is one that   
  receives mail from a transport service environment and passes it to a    
  mail user agent or deposits it in a message store which a mail user    
  agent is expected to subsequently access.  A "relay" SMTP system   
  (usually referred to just as a "relay") receives mail from an SMTP    
  client and transmits it, without modification to the message data other
  than adding trace information, to another SMTP server for further        
  relaying or for delivery.       
  
  A "gateway" SMTP system (usually referred to just as a "gateway")
  receives mail from a client system in one transport environment and      
  transmits it to a server system in another transport environment.      
  Differences in protocols or message semantics between the transport      
  environments on either side of a gateway may require that the gateway  
  system perform transformations to the message that are not permitted to  
  SMTP relay systems.  For the purposes of this specification, firewalls   
  that rewrite addresses should be considered as gateways, even if SMTP    
  is used on both sides of them.  

That is, if a system is "relaying", it must not modify the message. But
who declares that a particular host is a "relay"? I think this is a post 
hoc thing: IF a host receives messages AND transmits them without 
modification THEN it is a relay. Otherwise it's a gateway. Sounds like 
AOL is a gateway in this terminology.

> Outside of the question of RFC-legality, what do people think of AOL's
> Subject rewriting ("<" replaced with "<.") as a solution to their
> problem?

It's crap, of course.

-- 
Philip Hazel            University of Cambridge Computing Service,
ph10@cus.cam.ac.uk      Cambridge, England. Phone: +44 1223 334714.