Re: SPF is harmful. Adopt it.

JdeBP> Third: A message store is a server, whereas an SMTP Relay
JdeBP> puppet is a client.  The traffic patterns for the two are
JdeBP> noticably different.  And note that some organizations
JdeBP> _already_ put measures in place to prevent all machines, 
JdeBP> other than the ones that they specifically designate, 
JdeBP> from running public servers.

ILT> This is a good point.

PJH> Not that good. Many organizations already block port 25 outgoing.
PJH> Even some ISPs do that for their "consumer" DSL products.

And they get into trouble with their customers for doing it.  It's generally
considered to be an inept idea whose long term consequences have been ignored
by those who deploy it.  

It's ironic that you mention DSL.  "Consumer DSL" is almost always ADSL, and
the 'A' in "ADSL" is there precisely because the model is that customers will
generally be clients connecting to servers Out On Internet, and not be running
servers for the rest of Internet to connect to.  Customers become quite upset
when ISPs start dictating what servers they, as clients, can connect to, given
that that's their supposed rôle in ADSL.  But, conversely, they find
themselves on shakier ground, given the 'A', when ISPs prevent the world from
accessing servers that they themselves run.  (Of course, the bandwidth
asymmetry is not always tilted towards the client.  An ISP would have a hard
time defending a prohibition on running an MSOAP server on asymmetric
bandwidth requirements grounds, for example.  However, we are discussing MSRAP
servers here.)

Of course, a far better approach than foolishly and shortsightedly blocking
connections to particular remote ports is to move the world to a point where
it _doesn't matter_ that "edge" machines try to connect to SMTP Relay
services, since everyone will either be running Snubby The Mail Rejector or
simply not providing SMTP Relay service at all.