From: Douglas Otis [mailto:dotis(_at_)mail-abuse(_dot_)org]
This presumes bad actors are blocked by an easily defeated scheme.
Guidance offered by SPF suggests the numbers blocked is less than
3%. In addition, blocking is not as black and white as you
suggest.
What happens when someone sends a message to a mailing list?
This presupposes that the issue is blocking rather than cost control.
Spam filtering is a real cost. AOL, Gmail, Hotmail, Yahoo all use a very
significant amount of electricity feeding machines whose sole purpose is spam
control.
If we assume that 30% of the market is those three providers then 9% of the
emails sent are going to be internal between just those 3 email providers.
If we assume that the email bill for each email provider's spam control is $1
million a month the ability to whitelist email sent within just that group
translates to approximately $1 million per provider per year in electricity
saved alone.
That is not a bad ROI at all. and reduced carbon emissions.
Of course the senders are not stupid and they will avoid using those domains to
send spam to if they know that checking is in place. So the only spams that are
getting caught are going to be from the stupid spammers.
Checking a digital signature is much less expensive than any of the effective
spam checking schemes I know of. The ROI is not in the mail you block, its in
the mail you whitelist.
If you are a legitimate email sender you will find that addind a DKIM signature
to your message is cheaper than constantly dealling with the major ISPs to get
your mail server whitelisted. It also means that you can be protected if you
happen to find yourself co-located on the same box as a spammer without your
knowledge.
DKIM base is not about increasing rejects, it is about reducing the cost of
accepts.
DKIM policy is about deterring impersonation. The actual number of rejects is
not significant. In fact you want it to be low rather than high.
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