include lists

This approach relies on your building and maintaining a list of email addresses from which you will permit the receipt of email messages. If someone who is not on your list sends you an email message, it doesn't get through. Depending on whose software you're using to manage your Include List and the blocking of messages from people not on your Include List, messages which are blocked might simply be trashed or they might trigger the transmission of an automatically-generated message back from your PC to the sender of the message asking them to identify themselves as human. The idea here is that, if the message was a spam message, the spammer is hardly going to be bothered reading your automatically generated message and going through whatever hoops are required to identify themselves as human.

A couple of problems arise with this approach:

• It's very restrictive. Only people that you have on your Include List can send you messages. This is not very practical in the real world where genuine email often arrives from people from whom you might never have received an email previously (and who are therefore unlikely to be on your Include List). Imagine if the telephone network operated this way!
  
• It's a pain-in-the-butt for people who are genuinely trying to reach you. Receiving an automatically-generated response that requires them to complete a form in order to have the privilege of sending you a message is, well, arrogant (we think).
  
• Things are not much easier for anyone implementing this approach. It requires the download and installation of software (which does the blocking and generation of the automatic messages) and the ongoing maintenance and updating of the Include List.
  
• It can have unhappy consequences: If person X sends a message to person Y and X is not on Y's Include List, Y's PC will send an automatically-generated message back to X. But if X has installed a similarly simplistic approach to spam blocking and doesn't have Y on his or her Include List, X's PC will send another automatically generated message back to Y. And Y's PC will send yet another automatically generated message back to X and then…