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.
"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: