mail regexp pattern:
^[a-z0-9_-]+(\.[a-z0-9_-]+)*@[a-z0-9_-]+(\.[a-z0-9_-]+)*(\.[a-z0-9_-]{2,4})$
^[a-z0-9_-]+(\.[a-z0-9_-]+)*@[a-z0-9_-]+(\.[a-z0-9_-]+)*(\.[a-z]{2,})$