At first glance, your code looks ok (though I just glanced at it). A couple of thoughts:
How long ago did you create the “recipient” email address? I have found that it can take more than a full day for “new” email addresses to be “live”
I have also found that, for some unknown reason, it sometimes takes formmail some time to begin to work. I have no idea why this is, but I have actually “given up” and written support in the past because “formmail wasn’t forwarding mail”, only to have it start working several hours later (with no intervention from DH).
If you have re-checked your hidden fields, and you are sure everything is correct, I’d send a support ticket.