Turns out that what was causing the problem appeared to be an errant session variable. I had put two of them in the body of the email. One was the generated password, the other was the user's email address that I was pulling from the form. For some reason the user's email address was causing the problem such that UE wouldn't send the email.
I discovered this problem by deleting any of the dynamic values from the body of the email and then running the process of entering form data and submitting it. Sure enough, i got an email albeit without the dynamic values. Then I added just the password and it would send OK. Then I added the email address session variable and it failed.
So I guess it's working OK, I must have done something wrong with the session variable.