Sends a reply to the sender of the message that you are currently
    reading or to the sender of the last message you read. If you
    do not specify the name of a file to be sent as your reply, Mail
    prompts you for the text of your reply.

    You can use the ANSWER command and the REPLY command
    interchangeably because they work the same way. You must be
    reading a message in order to answer it.

    Format

      ANSWER  [file-spec]