This section steps through how to implement a simple protocol event sink for the EHLO SMTP command using the Microsoft Visual Studio 6.0 and the Microsoft Active Template Library (ATL 3.0). The "ShieldsUp" sink, when enabled, stops all inbound SMTP connections immediately after the arrival of the "EHLO" command from a client, returning a friendly error string such as "Please try again later." The full source code for this sink can be found in the examples section of this documentation.