Email Content filtering for offensive co

Greetings,

I’m looking for a product that will allow me to filter email content for offensive content. I’m a k-12 school and this is a requirement of E-rate. What is the best product out there for the $ and ease of use for the Administrator. Iuse an Exchange 5.5 Server and Outlook as the client.
I need to filter for porno, language content both for incoming and outgoing emails.

Thanks!
Michelle