There are filters, but it depends on your definition of 'know'. If you want to have docs with someone you know in real life, that's fine, and you can exchange emails with them and set your filter to block everything except stuff from him and other people you know.
But, you don't really know anyone on the HS forum. Anyone can lie about age, gender, etc. and you would have no way of knowing. Even with a throwaway email, you can still get persuaded by people through clever tricks to give away your personal info, which can end up in the wrong hands.