I don't believe there's a great way to do this through the dashboard itself. You may want to look at a Netflow configuration. In a nutshell, you'll tell your MX to send Netflow to a specified server/workstation with some Netflow parsing software on it (we use Solarwinds Netflow Traffic Analyzer). The software can then give you a rough breakdown of what traffic is passing through the MX, along with analytics like top talkers, top sources, top destinations, and specific information like throughput to/from a specific website or host.