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Re: Allowing MTAs to split messages to different recipients

2001-01-15 09:13:57
If a sender in Europe sends a message to two or more recipients in 
North America, only one copy might be copied across the expensive 
Atlantic cables as shown in the figure below:

A problem with this, however, is that most MTAs are not willing to
handle mail, unless either the recipient or the sender is local to
the MTA. 

There are more fundamental problems than this, namely, that the
sending MTA has no idea where its recipients are located with
respect to expensive links, so it has no basis with which to optimize. 

Thus, the saving shown above requires an agreement with the
MTA which splits the message after transport across the Atlantic.
This was not always so. 

True, but probably not relevant.

In the beginning of the 1990-s, most MTAs
were willing to forward mail for any recipient. The reason why this
was abolished in the middle of the 1990-s was that spammers used this
feature to get foreign MTAs to help them split mail to millions of
recipients. Some so-called experts claimed that spamming could be
stopped by forbidding splitting of mail by other than the MTA of the
sender or the recipient. They enforced their view by implementing a
program which scanned all MTAs everywhere, checking that they did not
allow foreign splitting, and sending angry letters to non-conforming
MTA administrators (postmasters) threatening to stop receiving mail
from them unless they stopped splitting. This is an interesting
example of how the Internet is regulated in dubious ways by
pseudo-police-authorities. Spamming could be counteracted more
efficiently using other methods than this.

While your history is reasonably accurate, I think you're mixing
two fairly unrelated things. And I don't think you've supported 
your last statement.  

In general it doesn't seem reasonable to expect an MTA to handle 
inbound traffic for other recipients than those for whom it's agreed 
to exchange mail.  Regardless of whether or not the traffic is spam, 
it's still taking up their resources.  To expect a remote MTA to
forward third party traffic, in the absence of explicit agreement
and permission to do so, strikes me as naive.  Even though at one
time it was a common practice, it's never been required by the 
SMTP protocol, and it was therefore never safe from the point-of-view
of application design to depend on this happening.  On the other
hand, if you get explicit agreement from remote MTAs to forward
your list mail (with either authentication or narrowly tailored
filtering for your list traffic), you can still do this.

To my way of thinking, the blacklists were indeed abusive.  They 
were mounting a distributed denial-of-service attack, using
propaganda and disinformation to entice gullible MTA administrators
into filtering using their criteria.  To me this is little better
than putting a virus in an executable attachment of an email message 
and labelling it in such a way that the recipient is likely to click
on it.  Perhaps they had good intentions, but some virus writers have
good intentions also.  In this case the attackers were naive 
about the likely good that it would do and about the harm that would
result.  But from my point-of-view the principal damage that was done was 
to thwart the legitimate use of SMTP for submission of messages by mobile 
users to their "home" SMTP servers.  (and no, SMTP-after-POP doesn't 
work reliably, and SMTP AUTH isn't widely enough deployed even now)

Keith