depending on your host you may need to set the SMTP Server address. Or you may need to set the From Address to be included as an extra parameter.
There are a couple of problem I see in your set up:
1) You have entered multiple to addresses and separated them by a coma. to enter multiple to addresses, you should click the To Button to enter the advanced To settings, and add each address individually.
2) on the attachments screen, you have added bindings for each of the form elements. the attachments section is to add file attachments, you should not be using the form bindings here.