You are the messaging engineer for your company. You have deployed four Exchange Server 2007 servers: a Mailbox server, a Hub Transport server, a Client Access server, and an Edge Transport server. The Edge Transport server is located in the perimeter network and receives all e-mail from the Internet. You need to recommend a solution to prevent internal users from sending e-mail messages with MP3 and WAV file attachments to each other. What should you recommend?