[extra88]

The point is the vast majority of regexes attempting to validate an email address will produce false negatives, reject valid email addresses. If a regex must exist, it should strip all whitespace characters first, confirm there is a single '@' with one or more characters before it, and two or more characters after it (the davidcel.is article mentions checking for a dot but a@us could be a valid address that would fail that test); it should not balk at character sets other than ASCII.

If you want to do some additional non-regex validation, like confirm the hostname exists and has an MX record, have at it.