Riva:
I would hope in this day and age a script could be written that locks a user account and moves the message(s) into a holding pen if x or more people report it as spam then ...
Sorry, too late! The spammer is encouraged. Pre-approval is the only way to effectively discourage spam.
The first essential requirement to avoid spam, which I seem to recall (as it has been a while) is in fact used here, is the necessity to register with an email address and return a token sent to that address. This is a good deterrent to "bots" and whilst an enterprising "human" can get through this hurdle, their email address can subsequently be blacklisted as they are removed.