There is a belief that there is a current task addressing this already.
However, we've just had an instance that made us think of it again.
How can we transform obvious errors in email address? Elliot mentioned that there is already something in place on the donation form to help with 1 character errors.
Possibilities include a Civi extension that lets you do a bulk search-and-replace on email domain names, e.g. gmail.con->gmail.com