efaq: Replying to the sender of a message

 
 11.6 How can I force Rmail to reply to the sender of a message, but not the other recipients?
 =============================================================================================
 
 Ron Isaacson says: When you hit <r> to reply in Rmail, by default it CCs
 all of the original recipients (everyone on the original ‘To’ and ‘CC’
 lists).  With a prefix argument (i.e., typing ‘C-u’ before <r>), it
 replies only to the sender.  However, going through the whole ‘C-u’
 business every time you want to reply is a pain.  This is the best fix
 I’ve been able to come up with:
 
      (defun rmail-reply-t ()
        "Reply only to the sender of the current message. (See rmail-reply.)"
        (interactive)
        (rmail-reply t))
 
      (add-hook 'rmail-mode-hook
        (lambda ()
          (define-key rmail-mode-map "r" 'rmail-reply-t)
          (define-key rmail-mode-map "R" 'rmail-reply)))