java script Email

IsEmail: Returns a Boolean if the specified Expression is a
          valid e-mail address. If Expression is null, false
          is returned.
 Parameters:
      Expression = e-mail to validate.

function IsEmail(Expression)

{

        if (Expression == null)

                return (false);

        var supported = 0;

        if (window.RegExp)

        {

                var tempStr = "a";

                var tempReg = new RegExp(tempStr);

                if (tempReg.test(tempStr)) supported = 1;

        }

        if (!supported)

                return (Expression.indexOf(".") > 2) && (Expression.indexOf("@") > 0);

        var r1 = new RegExp("(@.*@)|(\\.\\.)|(@\\.)|(^\\.)");

        var r2 = new RegExp("^.+\\@(\\[?)[a-zA-Z0-9\\-\\.]+\\.([a-zA-Z]{2,3}|[0-9]{1,3})(\\]?)$");

        return (!r1.test(Expression) && r2.test(Expression));

}