The Wanderer a écrit : > > When you hit Reply on an E-mail using a modern mail client (and quite a > few non-modern ones), in addition to generating a new Message-ID for > your reply, the mail client creates another header called "In-Reply-To". > It copies the Message-ID from the original mail into this new header. It also adds the message-ID into the "References" header, which contains all the thread history, so that missing messages won't break the thread.