My best guess is that it IS sending it but it is getting caught in a spam filter. Have you tried a different TO address? Does that work?
I'd need to debug to find the cause. The email almost certainly is being sent because the BCC recipient gets a copy. Does the TO field look correct in the BCC copy?
If you add that email address as a BCC or CC recipient does it then get the email?
If you give me FTP access I can debug further.