You can reply to a message with the r command. If you have just read a message, entering r at the mail prompt starts a response to that message. If you have not read any messages, typing r begins a response to the current message (shown by the status flag ``>''). You can also reply to a particular message by typing r number, where number is the message number.
When you respond to a message, mail automatically fills in the ``To'' and ``Subject'' fields for you:
&If you did not intend to reply to a message, or you change your mind, enter ~q on a new line to abandon the creation of the response.
r 12To: peterp Subject: Re: XTR work - can we hold meeting?
r replies only to the sender of the message. If you want to respond to the sender and everyone who was copied on the original mail, use R instead.
If you want to change any of the header fields while you are composing your reply, go to a new line and type ~h. You can then change any of the header details. See ``Editing a message's header''.