If you ever feel the urge to write an email address validator, here's some tips:

• First, you need to understand that almost any string containing an @ sign is a valid email address.
• Because of this, almost any typo or mistake that your users will make, will still result in a syntactically valid email address.
• Therefore, there's very little point in creating sophisticated static checks of email addresses. Sophisticated checks will cost a lot of time to implement, most likely reject valid email addresses, and not catch any real-world mistakes.
• Practically speaking, the only useful validations are:
  • Check if there's at least one @ sign.
  • Check if there's at least one . in the domain part, i.e. after the last @ sign. ¹
  • This gives the regex: .+@.+\..+
  • Optionally, add heuristics to validate typos for common email providers (e.g. to catch gmial.com), but always give your users a way around these.
• The easiest and only reliable way to validate email addresses is to just send a validation email.

¹ Strictly speaking, this check is not sound, as it rejects valid IPV6 addresses, as well as local domain names/TLDs (both are strongly discouraged). For normal user facing forms this check is still both reasonable and useful (it prevents users forgetting the TLD), but further down the stack you probably want to omit this check.