//Ther are three type of REGULAR EXPRESSION     
   //first
   ^(.+)@(.+)$   "^(.+)@(.+)$\""
   //second
   ^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6}$
     //third
   ^[\\w!#$%&'*+/=?`{|}~^-]+(?:\\.[\\w!#$%&'*+/=?`{|}~^-]+)*@(?!-)(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,6}$