Well u can regularly monitor all your uploaded files and folders.You should not open those websites which are of high risks to spams.Be firm but rational. Remember, your customers may not be savvy about spam; they could have left their accounts open to someone else to use.

__________________
wipr
Wipro Dedicated Servers

Education is key to both your staff and customers. Keep up with the trends and technology spammers use. Teach your staff what to look for in new customers and why you do it. Set firm policies about using company email such as restricting use for business use only.

Check customer IP’s and domains against blacklists or search in Google or Google Groups. If a domain is not registered, be cautious. When checking up customers, remember to look out for address or telephone number match also.

If you currently have instant account activation, you may want to review how effective it is for your business. Spammers love this because they can quickly set up an account, send thousands of spam and be on their way again. By the time you find out, the damage has been done. By all means have a quick and easy account activation procedure but work in a manual approval step.

Have SMTP authentication turned on and ensure your servers are not used as open relays. If you have form mail scripts for customer use, make sure you are using a secure one.