Hi Yurii,
You won't be able to replicate as you need to log in as a user with messages. I can set this up for you but may be easier to explain in the picture I have put together below. The "(NEW)" is not showing after the Subject as you can see. I have also tried this function with same result.
if($(this).find("[name=lblMsgRead]").text()==='false'){
return value + '(NEW)';
}
else
{ return value;}