The previous section illustrated why a recipient can’t stop spam alone. The example showed a service provider with a strong anti-spam policy but with little way to catch an abuser if left to their own devices. It also showed a mail server in another country being used to relay the spam. In both cases, service providers had to be contacted in order to deny the spammer the tools of the trade.

The lesson to be learned is that service providers have both a responsibility and a vested interest in reducing spam. The means by which service providers attempt to control spam come in two flavors: MTA controls, which are technical means of control, and contractual controls, which are social ones.