Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!PT.CS.CMU.EDU!andrew.cmu.edu!cfe+ From: cfe+@andrew.cmu.edu.UUCP Newsgroups: comp.emacs Subject: Re: GNU Emacs vs. sendmail - battle of the titans Message-ID:Date: Mon, 7-Dec-87 16:10:34 EST Article-I.D.: andrew.UVilZ-y00VsLYwY5D5 Posted: Mon Dec 7 16:10:34 1987 Date-Received: Sat, 12-Dec-87 16:14:49 EST Organization: Carnegie Mellon University Lines: 18 In-Reply-To: <8712040000.AA05718@PTT.LCS.MIT.EDU> RFC-822 does indicate a standard order of fields to reply to, but it isn't all three of those. It's to use the Reply-To: field, if present; otherwise, the From: field. You never reply to a Sender: address. What I mean by ``reply to'' is that when a user asks to reply to a message (say, X), then the user's mail agent may assist the user by providing values for the fields in the header of a new message. Typically, the To:, Subject:, and In-reply-to: (if not also References:) fields are derived from the fields of message X. When the mail agent provides a value for the To: field, it should use the value that was in the Reply-to: field of message X, or the From: field of message X in case message X had no Reply-to: field. (Whether the user agent makes use of the contents of the To: or CC: fields of message X is pretty much up to the user agent.) This case is different from a system's automatically returning an error message to the sender of a piece of mail. In that case, RFC821 and RFC822 technically disagree, but what it's come down to is that you return the mail to the argument of SMTP's MAIL FROM: command, if you got the mail via SMTP.