When I, as an admin, create a new user, if I mistakenly provide an invalid email address in the email field for that user, will I get any failure notification or email from Salesforce? Is there any way for me to know that the email address I provided was invalid?
However, if you're talking about an incorrect e-mail address. I've not had any notification from Salesforce when submitting one. Presumably you'd need to liaise with the user if they haven't had their password creation e-mail and double-check the e-mail they gave you is correct.
Hope this helps!