How about we look at a case where the forwarder has no profit, just cost:
debian.org. Many debian.org users use their addresses as a general
purpose
address, with the intention that they will always have it, to forward
wherever they go.
OK, debian.org are providing the "appearance" of a mailbox for no charge.
Jolly good. Well done.
In many
particular cases, that 3rd party is a large ISP corporation that has no
profit motive to let end-users selectively disable filtering of some of
their mail. Thus, debian.org, ostensibly an agent of the recipient, is
forced to bear a cost (taking responsibility for the message in the eyes
of
the recipient ISP) in place of the sender.
Indeed, that's the point. debian.org *are* sending this mail to
isp.example. They're doing this as the agent of a person who is a customer
of isp.example They are not doing this *for* isp.example, they're doing
this *to* isp.example
isp.example hold debian.org responsible for sending it. What's wrong with
that?
If isp.example users can't modulate the filtering behaviour to pass-thru
the debian.org routed stuff and some LMAP-thing is active - this will be a
hostile environment for forwarding. debian.org have a number of
alternatives:
1. do the rewriting (and accept some implied responsibility?)
2. refuse to rewrite and get blocked by systems which don't like the look
of mail from example.com routed via debian.org
3. Provide a real mailbox, POP / IMAP.
Perhaps what we need is some standardized way for the
recipient/forwarding
user to authorize the message in advance of any filtering. Unfortunately,
that probably won't be effective in this case unless we got an ESMTP
extension designed for it, because ISPs want to filter as early as
possible
in the transaction.
Ideally, a system running LMAP-thing should give users the ability to
configure it in such a way as not to be forwarding-hostile. If there's no
"profit-motive" for supporting this, it suggests that customer demand is
too small.
I'm very much in favour of some standard for configuring filtering at the
ISP. However, I can't see how one could make this a pre-requisite for LMAP
deployment.
It seems possible that widespread adoption of LMAP-like systems could
increase costs for forwarders. I don't believe there's a rule which says
that the forwarders p.o.v. is more significant than the receiving ISP's.
The feature that allows debian.org to forward transparently has costs.
Spome of these costs are currently borne by mom&pop.example.com when their
little mail server chokes on 50k bounces an hour from yahoo for spam they
didn't send.
The costs of spam at isp.example are passed onto the user, they have a
business model which supports this. If the forwarder doesn't have such a
business, they may have to reconsider the services they offer.
Omelette v. Eggs, I suppose, or, better, TANSTAAFL.
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