Assymetrical Relationships

IM2000 brings the problem of assymetrical relationships to a new and
interesting level, so it might be important to study and directly
address it in any proposed implementation.

By "assymetrical relationship" I mean that, given two parties, A and
B, B might permit A to initiate contact to it, but A might not permit
B to initiate contact to it.

With push-delivery email, that isn't generally a problem, unless B
wants to send a new message to A responding to a message A
sent...which brings me to the problem SMTP has with its receiver-side
notification scheme (bounces), in which bounces sometimes cannot be
delivered.

(For example, if [email protected] sends email to [email protected],
my system generates a bounce, but cannot deliver it, since aol.com
ordinarily blocks incoming SMTP connections from my system.  I do have
a patch to qmail-remote to cause delivery attempts to fall back to my
upstream ISP, but, due to the proliferation of joe jobs and my feeling
that bounces are a *courtesy* to a sender, it doesn't engage that
mechanism for bounces.)

For IM2000, the problem could manifest itself for different reasons,
and hopefully anti-UBM measures won't be one of them.  (That is,
there's little reason to block incoming *requests* for message from an
outgoing message store, though there will be plenty of reason to block
incoming *injections* of messages to it.)

Still, implementors and admins should be given clear instructions as
to the importance of not blocking incoming requests pertaining to the
outgoing message store under any circumstances, *or*, if they do, to
make sure "holes" are punched in whatever blocks they set up that
pertain to any messages actually sent out.

(These "holes" can't pertain to a recipient's IP address or anything
like that, since the recipient can, and will, roam, e.g. on a laptop
with his message notifications available.  So they have to pertain
only to the legitimate messages that recipient might want to fetch.)

Of course, failure to assure recipients that they will not be blocked
accessing their own incoming email would be a serious problem for
IM2000, one with which they're not already familiar.

Similarly, once a message has been accepted for delivery by an agent,
access by the sender to that agent, in order to query it regarding the
status of delivery, must always be allowed, at least to the extent the
original access was allowed.  Failure to assure this would be more of
an annoyance than a serious problem, since the failure mode would be
that senders would redeliver important messages via other means.

-- 
James Craig Burley
Software Craftsperson
<http://www.jcb-sc.com>