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.105Read RFC-1437 if you don't believe this statement!106Guylhem can be reached at guylhem@danmark.linux.eu.org. 234This administrative data falls into two categories.In the first category is any data that is specific to the transportmedium, like the address of sender and recipient.It is therefore called the envelope.It may be transformed by thetransport software as the message is passed along.The second variety is any data necessary for handling the mail message, which is not particular to any transportmechanism, such as the message's subject line, a list of all recipients, and the date the message was sent.In manynetworks, it has become standard to prepend this data to the mail message, forming the so-called mail header.Itis offset from the mail body by an empty line.107Most mail transport software in the Unix world use a header format outlined in RFC-822.Its original purposewas to specify a standard for use on the ARPANET, but since it was designed to be independent from any envi-ronment, it has been easily adapted to other networks, including many UUCP-based networks.RFC-822 is only the lowest common denominator, however.More recent standards have been conceived to copewith growing needs such as data encryption, international character set support, and MIME (Multipurpose Inter-net Mail Extensions, described in RFC-1341 and other RFCs).In all these standards, the header consists of several lines separated by an end-of-line sequence.A line is madeup of a field name, beginning in column one, and the field itself, offset by a colon and white space.The formatand semantics of each field vary depending on the field name.A header field can be continued across a newlineif the next line begins with a whitespace character such as tab.Fields can appear in any order.A typical mail header may look like this:Return-Path:Received: ursa.cus.cam.ac.uk (cusexim@ursa.cus.cam.ac.uk [131.111.8.6])by al.animats.net (8.9.3/8.9.3/Debian 8.9.3-6) with ESMTP id WAA04654for ; Sun, 30 Jan 2000 22:30:01 +1100Received: from ph10 (helo=localhost) by ursa.cus.cam.ac.uk with local-smtp(Exim 3.13 #1) id 12EsYC-0001eF-00; Sun, 30 Jan 2000 11:29:52 +0000Date: Sun, 30 Jan 2000 11:29:52 +0000 (GMT)From: Philip HazelReply-To: Philip HazelTo: Terry Dawson , Andy OramSubject: Electronic mail chapterIn-Reply-To:Message-ID:Usually, all necessary header fields are generated by the mailer interface you use, like elm, pine, mush, ormailx.However, some are optional and may be added by the user.elm, for example, allows you to edit part ofthe message header.Others are added by the mail transport software.If you look into a local mailbox file, youmay see each mail message preceded by a "From" line (note: no colon).This is not an RFC-822 header; it hasbeen inserted by your mail software as a convenience to programs reading the mailbox.To avoid potential trou-ble with lines in the message body that also begin with "From," it has become standard procedure to escape anysuch occurrence by preceding it with a > character.This list is a collection of common header fields and their meanings:From:This contains the sender's email address and possibly the "real name." A complete zoo of formats isused here.To:This is a list of recipient email addresses.Multiple recipient addresses are separated by a comma.Cc:This is a list of email addresses that will receive "carbon copies" of the message.Multiple recipient ad-dresses are separated by a comma.107It is customary to append a signature or.sig to a mail message, usually containing information on the author along with a joke or amotto.It is offset from the mail message by a line containing "--" followed by a space 235Bcc:This is a list of email addresses that will receive "carbon copies" of the message.The key difference be-tween a "Cc:" and a "Bcc:" is that the addresses listed in a "Bcc:" will not appear in the header of themail messages delivered to any recipient.It's a way of alerting recipients that you've sent copies of themessage to other people without telling them who those others are.Multiple recipient addresses areseparated by a comma.Subject:Describes the content of the mail in a few words.Date:Supplies the date and time the mail was sent.Reply-To:Specifies the address the sender wants the recipient's reply directed to [ Pobierz całość w formacie PDF ]

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