User maintainable blacklist?

[Andy Alsup]

Are there facilities for having users maintain a blacklist?  Either web
based, or by e-mail forwarding?

I have thought about doing a blacklist at myemailserver mailbox, and
building a blacklist based on any mail forwarded to this address that's
not from a legit user.  If the address gets spammed, that works too!
Users would just forward spam to this address before they delete it.

Has anyone done anything like this, or is there an existing work in this
area?

I'd like to do a whitelist in a similar way, but that address would have
to be protected somehow.

Thanks.