SPAM filtering MUST be implemented as voluntary opt-in, otherwise it will be
illegal, as you correctly notice. Spam-filtering can only be legal when
it is performed strictly on behalf of the recipient, the receipient is
in full control over the behaviour all the time, and the blocking or
deletion of any messages is performed with explicit and voluntary
(i.e. condition-free) consent of the receipient himself.
If that were true, there would be no Gmail, Hotmail, or Yahoo mail users
in Germany, since they offer only limited control over spam filtering, and
some stuff, e.g. DNSBL blocks, is unconditional.
I expect that the mail systems make it a condition of subscription that
the recipients consent to the mail system doing whatever it has to do to
filter incoming mail.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
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