Whitespace in front of the @ is only allowed within quotes, and any quoted part must be seperated by dots from unqoted parts. "my address"@example.com is allowed, as is my." "[email protected], but not my"address"@example.com.

Once you get that into a regex format, remember that a quoted dot is different from an unqoted dot, and don't forget that you handle comments within email addesses correctly.

There are plenty of reasons why people say not to use regex to validate email addresses.