I got asked recently about email validation: is "+" valid?
Yes, the plus sign is a legal character in an email address. Though even if it were not, you'd do well to accept that character since it's used by millions of Gmail users:
Many surprising characters are legal in an email address. Pretty much everybody gets email validation wrong.
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"Stop Validating Email Addresses with Regex"
ICANN test for legal internationalized email address characters
If you still want to take a shot at evaluate the correctness of an email address string, at least do it with library that uses a parser and has attempted (nevertheless imperfectly) the difficult task of complying with all the relevant RFCs. For example: