Most web browsers remember the email address that was entered on login forms or even on signup forms their email might be pre filled for them. But it's true if

Most web browsers remember the email address that was entered on login forms or even on signup forms their email might be pre filled for them. But it's true if the user enters the wrong email address and then never notices it's incorrect, could result in a problem later down the road if the email address is a login. Perhaps a notification after a few days along the lines of "verify your email address is correct" top of the page in cases where it appears they haven't received your welcome email would be more appropriate. Rather than barricading them from using the service.