1. 'From' should be an email account on your domain
2. Check that email account for bounced emails
3. Hotmail and some others bounce emails from x10hosting's servers due to the abuse by a few. They do not even end up in the spam folder.
4. On other providers, check the spam folder.
5. You are not checking the return value of mail(). How can you say it is saying the mail is sent?