Hi,
I only subscribed to this list yesterday so apologies if this idea has
already been covered:
The spec describes the ability for individual domains to choose when/if to
begin rejecting non-SPF and/or 'softdeny' mail sources as basically an on/off
option.
There is a half-way house (or 'twilight period') of downgrading the delivery
speed. Basically this involves a technique similar to 'greylisting', where
mail of questionable origin is rejected with a temporary failure "451 Please
try again later". On subsequent re-try attempts by the sending MTA the mail
will be accepted.
This can be used to create a 'second-class email' category for non-SPF mail
where delivery is delayed. As time goes on, the pressure on those not in
compliance can be ratcheted up by slowly increasing the delay period. For
instance begin with a 1-hour delay and add an extra hour each month.
After a year, the delay would be 12 hours etc... SPF-enabled MTA's can even
use the current date to calibrate this so that admins don't have to bother.
Further more it is the sending (non-compliant) MTA that feels the pain of having
to queue all of these delayed emails. Secondly many current spam tools do
not attempt redelivery so a great deal of spam will be stopped completely right
from the start.
- Dan
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