Comment by ashley95

This is cute and all. But for anyone coming here for real-world advice: just use a regex, normalize to lowercase, and surface any errors to users so they know if their email got rejected. This will avoid 99.9% of issues and work for 100% of real human users. This is what everyone else does, and if you have a user with an esoteric email, they will still be able to furnish another one that passes this validation.