js 验证邮箱地址合法性

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));
}