How to Analyze User Traffic by Internal or External Destination

After writing a previous article about using PowerShell to analyze message trace data, I was asked about analyzing user (or mailbox) sending patterns to discover who's sending email and where they're sending messages to. As in many similar situations, PowerShell is a great tool to use because of its flexibility. This article explains how to generate a per-mailbox report of how many messages are sent and the percentage of internal versus external, plus the external domains the email goes to.