Help with PHP Mail Function/Checkbox Output

I'm about to yank out my David Powers book library but I figured I'd post here in case I can't locate it.

I'm trying to manipulate the output of checkboxes in DW. I'm using PHP and when the checkboxes are selected they come thru outputted (in an html email) as "on".

So if 3 are checked is shows as "ononon". I've double checked the labeling, what am I missing?

Thanks!!!!