The current selection filter is badly designed, and leads to improper delivery.  (See case 00673988 for details)

If you select ONLY the captains checkbox, the captains are the only folks who will receive the email.

Why wouldn't the opposite be the case if the box is left unchecked? We know that there's a boolean in a participant's record that determines if they are a captain on the event in question. Surely that is the piece that's hooked when the box is checked.

The first three items on the list of checkbox should be mutually exclusive:

* Individual participants not on a team
* Team members
* Team captains