No anti-UBM measure for SMTP-based electronic mail works. The real technical solution therefore has to be to redesign the mail system architecture so that either
IM2000 incorporates the latter, by redesigning the mail system as a pull delivery rather than as a push delivery system. (There are other ways of achieving the goal, too, but they have problems with the cost of enforcement.) Senders bear the costs of storing the mail that they send.
IM2000 does not directly incorporate direct recognition of unsolicited and bulk qualities. Instead it eliminates part of the very concept of bulk mail by employing an architecture whereby multiple copies of messages, even of messages sent to many recipients, do not actually exist in the first place until the recipients actually request the senders to make them.