Hashing spam

I work on an approach to block spam with a database of hash (md5) string of
spam email:
1) Reporting a "verified" spam to the database server on the web
2) the mail client check incoming mail, generate a hash string send to and
verify the presence on the server, is yes block email.
3) download a hot list to block directly on the machine

i don't know if it's a good or bad idea.

--giuseppe