I will try your suggestion of checking for NULL. However when I open the email log with SQLyog I do not see (NULL) in the email address field, I even clicked on the field wondering if I might see that a space was entered by accident.
Yes the invalid email addresses are in a valid format. I know there are some that should be bouncing because I had manually (import addresses into MS Outlook) sent to the same address list prior to using WA UE. I received 50 or so failure notices to the same return address as the one I'm using with UE.