richard at belcarra
Oct 9, 2003, 9:07 AM
Post #2 of 4
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One aspect of spam noted by a friend of mine in the computer security
business is that many spam programs don't re-try if they get a soft
error the first time.
His initial thought was to introduce a cycle in the MTA that would
reject all unknown sender/IP address combos the first time and allow
them the second within a (relatively) short period of time (say 1 hour
or 4 hours) since most spammers either don't retry at all, or retry the
next "cycle" which may be many hours later if they are in the millions
of addresses league.
This aspect is due to the fact that the spam program doesn't run a
"normal" MTA - one which retries as a rule and backs off on retry time
to longer and longer times over a matter of days.
richard
On Thu, 2003-10-09 at 08:26, Dan Boresjo wrote:
> 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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--
Richard C. Pitt C.E.O. Belcarra Technologies
richard [at] belcarra direct: 604-644-9265 www.belcarra.com
Embedded Systems Communications Specialists - USB, ATM, LAN/WAN, Wireless
USB for Linux, Windows, MAC OS/X - USBLAN (tm) - drivers for USB mass storage
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