Replying with a Selected Message

  Choose Reply Using Selected Message from the Create-Send
  menu to include the selected message in your reply.

  Mail opens a Create-Send window.  Mail automatically
  enters information in the To and Subject entry boxes, based
  on information in the original message, and displays the text
  of the selected message in the message area.  You can edit the
  message.

  Click on the Send button to send the reply.

  Additional topics:

  *   Including a File in a Message (no editor)