AS per my understanding most probable will cover by..
/^([a-z0-9_-]+)(@[a-z0-9-]+)(\.[a-z]+|\.[a-z]+\.[a-z]+)?$/is
AS per my understanding most probable will cover by..
/^([a-z0-9_-]+)(@[a-z0-9-]+)(\.[a-z]+|\.[a-z]+\.[a-z]+)?$/is