First time I've seen someone create a validator by simply matching against URI::MailTo::EMAIL_REGEXP from std lib. More often you see people copying and pasting some really long regex that they don't understand and is probably not loose enough. It's much better, though, to simply reuse a standard one from a library — by reference, rather than copying and pasting!!

If so, why then not use ProtonMail that does not serve ads, abuse your data, and gives you the option for built-in e-mail encryption?