The email of the contact person. It must contain '@' and dot '.' in form userid@hostname (50 characters maximum). The userid can be alphanumeric characters, '.', '-', or '_' but must begin and end with alphanumeric characters. The hostname can be alphanumeric characters, '.', '-', or '_'. It must contain at least two domain items. Every domain item should begin and end with alphanumeric character, and the last domain item should be 2-20 alphabetic characters.