This is a common problem. In cPanel/WHM, you can limit the number of mails that can be sent from a domain in an hour. In windows or plesk, you cant do that. Windows 2003 is not a server operating system you know, it is just more of a secured (or so called) PC. You cant expect any features in it.

Though you can set limitations in the number of mails send per domain, spammers get hold of scripts that clients use in their websites to send mails, and spam the hell out of your server. And your server just stops working. Or, if your server is powerful enough, your mails just stop working.

Whats the best way to prevent that from happening? Use google’s google apps. The free email service for your jenifaa-sakura domain name.

When you create hosting, make your settings in such a way that the mx record that is created for each domain is set to google’s. When your client gets the hosting, ask him to sign up at google.com/a and get his mail box. There he will have no limitations of mails or mail ids or anything. And there is no way that your IP gets blacklisted.

And google has a great system that they dont let people abuse their systems easily. It is a neat system.