Fundamental Anti-Spam Techniques
In this section, we cover some of the common methods used to defeat spam. These techniques show up many times throughout this book and are the basis of the ongoing fight against spam.
Whitelists and Blacklists
These are lists of senders who are always allowed (whitelisted) or always denied (blacklisted) the ability to deliver messages. These whitelists/blacklists are less useful now than they were when spam first became a problem, but they can be helpful in some circumstances. Depending upon how they are implemented, whitelist/blacklist checks can happen at one or more points along a message’s journey. For example, list checks can happen at the edge of the network, at the POP/IMAP server, or at the email client. ...