Replying to the Current Message

  Choose Reply from the Message pop-up menu to display
  a Create-Send window in which you can enter a reply to
  the current message.  Mail automatically enters some of the
  address information in the Create-Send window.

  In the To entry box, Mail inserts the name of the sender of
  the original message.  In the Subject entry box, Mail inserts
  RE: followed by the subject of the original message.

  Additional topics:

  *   Using a Create-Send Window