I am still "testing" before going to a dynamic To:.
I enetered the To: email address in the To: section of the email setup and get nothing when I submit the form. If I hardcode theTo: in the template it works.
To test a dynamic To: I placed the email address in a hidden field and used the wizard to generate the php string to retrieve the posted value... and got nothing when I submitted the form.
Looking at the logs in my SMTP mail server, I see the initial receipt, but somewhere to "$MailTo" field used in mail() is not being generated and the mail server is dropping the request.