[exim] quick help: headers_add question

Hi,

I'm trying to add a Sender header to my outgoing messages because one never
shows up. I want the Sender email address to be the same as the Reply-To
email address. Here is what I have in my router:

headers_add = "Message-Id: <E$message_id@$primary_hostname>"\n\
            "Sender: $header_reply-to:"

I'm not sure if \n\ is correct for a new line/header nor do I think I did
the Sender header correctly. Any help is greatly appreciated.

Thanks!

JP