Most European countries have laws against any email that is not the result of an existing "consensual" relationship. Even if you publish your mail address, you can sue persons who use it for other purposes than intended, and continue to do so after your protest. Spammers therefore use servers outside Europe and try to hide their business relations. Needless to say, spam continues.

In my opinion, all emails should have an "electronic signature" that is recognized by the authorities worldwide (though the sender may remain anonymous towards the receiver, if the latter accepts such mails). Suing spammers will then be almost automatical, since the proof is built-in.

The system already exists, but costs a little money. As soon as it is free, I will no longer accept any unsigned mails.