Of course, the best way to block unwanted email is with an allowed email list. You don’t need firewalls, you don’t need keyword searches, you just need an address book of people who are allowed to email you and a simple filter. The problem with this approach is that, if someone doesn’t make it into your address book, they can’t send your emails. This means that, for example, long-lost friends can not catch up with you over your email. More importantly, if one of your existing friends or clients changes his or her email address unexpectedly, you will lose contact. This can be quite costly to say the least.