this is due to a bug that i have logged in our bugbase to be corrected in a future update to CSS Form Builder.
When accessing the Universal Email settings by clicking the Edit Icon on the Form Functions tab of the CSS Form Builder wizard, the DW Edit Icon is missing.
if you set the Form Builder wizard to send the form contents in an emil then edit the Universal Email settings by Double clicking the Universal Email server behavior in the server behaviors window (Window -> Server Behaviors) the DW Edit option will be available.
also if you add Universal Email manually by going to Webassist -> Create Email Message, the DW Edit icon is available.