This paper describes a new approach to anti-spam techniques. Instead of having spam filtering software implemented at a mail client or server, we build a mail server agent called MT Proxy to deal with any spam related issue. This server acts a mediate firewall to securely protect our real SMTP mail server. All emails are allowed to come to their recipients, but at either slow or fast speed, depending on their spam characteristic. A key advantage of this prototype is having a system, which is capable of controlling, but not blocking email traffic. As a result, MT Proxy software is guaranteed not to make any spam decision mistake. On the other hand, the software can effectively slow down email connection from spam sources; which in long term causes an economic loss for spammers.