Tarpits&Transparent SMTP proxy

Tarpits

A tarpit is any server software which intentionally responds pathologically slowly to client commands. By running a tarpit which treats acceptable mail normally and known spam slowly or which appears to be an open mail relay, a site can slow down the rate at which spammers can inject messages into the mail facility. Many systems will simply disconnect if the server doesn't respond quickly, which will eliminate the spam. However, a few legitimate e-mail systems will also not deal correctly with these delays.

Transparent SMTP proxy

Transparent SMTP proxies allow combating spam in real time, combining sender's behavior controls, providing legitimate users immediate feedback, eliminating a need for quarantine.