Re: Everyone Greylists Except Honeypots ... So Let's Not Spam Honeypots!
On Dec 5, 2007, at 6:51 PM, John C Klensin wrote:
This type of reasoning is exactly the reason why some of us are
skeptical about greylisting and any other technique that works well
only if it is used by sufficiently few people. If it starts being
used enough, the spammers have the incentive to figure out how to
simulate the behavior that gets past the traps and then, sooner or
later, it isn't worth bothering with. The skepticism leads some of
us to wander away from conversations about how wonderfully effective
the technique while muttering "arms race". Others wander off in a
slightly different directions muttering "making the bad guys smarter
is really not a good strategy"
At least the first of those sources of muttering noises does not
suggest that you shouldn't use a method that works for you as long
as it does work for you (others might disagree about that). It does
mean, I think, that you should be somewhat careful about praising
the method to others or assuming that it will last forever. And
then there is the part I worry about most, which is that we will
make basic changes to the email protocols in order to make things
work better, for a short time, for these relatively short-life-
SMTP's inability to reliably identify where a message originated has
caused inordinate reliance on content filtering. While at first,
content filtering had been fairly effective, this in turn has caused
spammers to improve their obfuscation techniques at a rate that has
become impractical for receivers to match with resources.
For each direct source of spam, there are 4 sources of spam emerging
from tens of millions of MTAs as DSNs. The abuse of DSNs is seriously
eroding email's integrity.
Few MTAs can operate and accept message for all recipients. The
inability for MTAs to handle all possible traffic exposes valid
recipients to being discovered.
Providers of domain names, IP addresses, or certificates have a
conflict of interest, and are unable to prevent access to spammers.
SMTP can not even mandate the use of an MX record to avoid searching
for policy records.
Reputation assessments of the last hop IP address is causing spammers
to merge their traffic with other domains. Often this merging is
accomplished through compromised residential systems. The doubling
rate is at six months, quickly making last hop reputation assessments
While DKIM attempts to provide essential transport information, it is
also prone to replay abuse and employs public key cryptography where
sign-once / send-many gives transmitters a resource advantage.
Grey-listing does not afford any long term strategy. However, the use
of temp errors can help avoid a complete denial of service as a triage
strategy for limited receiver resources. Reputation is then used to
establish priority. Processing undesired messages can exceed 99% at
very high volumes. This is not how the Internet should work. A basic
change to SMTP is needed to shift the burden toward the transmitter.
Greylisting increases the number of transactions per message, so
ultimately, this is headed in the wrong direction.
The TBR reference exchange can be done within a single transaction.
The transmitter is required to hold messages until the receiver is
ready. With a high level of source granularity, message origination
reputation should be able match the transmitter's level of abuse and
not breed super spam. References can be retained for a period of
time, where abuse pattern can be detected and used to silently expunge