Hi Dennis, Currently, there isn't a notification that you will receive if the email is entered in error. As long as it is in the proper format (firstname.lastname@example.org) the system will try to send it. If you perhaps misspell the name of your client, they will need to let you know that they haven't received your email or you can select the option to "receive an alert when the user downloads" and you can tell in that way.
I apologize for the inconvenience.
Please let us know if you have any other questions.