Wait a second. Back up. Let's be clear here: the case you are talking about is the user entering their own email address incorrectly, and you're saying we as designers/developers should make a system that knows this and sends it to the correct email? What? Huh? If Person@place.com and person@place.com are two different recipients, how the hell is my application supposed to know which one you actually mean!?
The same way we deal with all email validation. Verify it once at application signup, then rely on the precise verified form.
It is unrealistic to expect end users to get the capitalisation of their email address consistently right. It is realistic to expect it to be done right at signup, since in the best practice case this’ll include a verification loop.
