Hello, In terms of technology, There must be a secure method that would allow a receiver to verify whether or not the sender actually exists as a user on the mail server for the domain the e-mail is coming from. Advantages: What I described above would allow mail servers to reject e-mail coming from randomly generated e-mail addresses and e-mail sent from anonymous remailers because the user has to exist on the mail server for the sender domain before the recipient's mail server is allowed to receive the message. So instead of receiving 1000 messages, the exchange above has to happen before any messages are received. This helps with the bandwidth problem. Disadvantages: What was described above does not prevent a user who actually exists on a mail server to send spam. It also doesn't prevent a sender from intercepting packets from the receiver and forging a response back to say that the user actually exists on the system when in reality the user does not. I am eager to hear everyone's comments on this.