% diagram 3

\verbatim
To: <reply-to|from>
cc: <??to|cc><to>,<cc>
Fcc: +outbox
Fcc: <??fcc><fcc>
Subject: <??subject>Re: <subject>
In-reply-to: <??date><??message-id>Your message of <date>.
	     <message-id>
In-reply-to: <??date><!message-id>Your message of <date>.
--------
?endverbatim