Changes between Version 4 and Version 5 of fr:Documentation/What is e-mail


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Oct 21, 2013, 10:06:07 PM (14 months ago)
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AmigaPhil
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  • fr:Documentation/What is e-mail

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    22[[TOC]]
     3
     4= Basics – what is e-mail?
     5
     6E-mail was the first service to be implemented on the Internet and
     7is still the most popular method of communication over the Internet.
     8A substantial proportion of the people on the Internet use only this
     9service.  It is predicted that in the next few years e-mail will replace
     10the traditional forms of communication like letters and fax for many
     11purposes.  At the present time one can in a matter of minutes reach
     12several million people world-wide by e-mail.  Users of other networks,
     13such as Compuserve and T-Online, are connected to the Internet through
     14"gateways".
     15
     16[[=#FixHeader]]
     17== Make up of a message header
     18
     19Every e-mail starts with a header which is separated from the
     20actual message body by a blank line.  YAM constructs this header
     21automatically following the settings specified in the configuration.
     22
     23The header of an e-mail is divided into fields which each start on
     24a new line and have the general form 'Field: contents'.  Fields which
     25are too long to fit in a single line can be split to run over several
     26lines.  The majority of the header lines can be omitted but are added to
     27provide the recipient's mail program with additional information about
     28the message or to give data needed to check for errors caused by
     29transmission problems.  A few of the important fields are explained by
     30means of the following example.
     31
     32{{{
     33  Return-Path: <just@zfn.uni-bremen.de>
     34}}}
     35
     36This field is added by the recipient's mail server and contains
     37the e-mail address of the sender to allow the recipient's computer to
     38send a reply by e-mail.
     39
     40{{{
     41  Received: from ina.zfn.uni-bremen.de by atlantica.access.ch
     42            (8.8.5/INA-1.05pri) id XAA29100;
     43            Tue, 23 Dec 1997 23:40:45 +0100 (MET)
     44  Received: from moritz37.zfn.uni-bremen.de by
     45            ina.zfn.uni-bremen.de (AIX 3.2/UCB 5.64/ZFNserver) id AA26355;
     46            Tue, 23 Dec 1997 23:40:13 +0100
     47}}}
     48
     49Each computer which sends the message on the next stage of its
     50journey, and also the recipient's own system, adds on a "Received:"
     51field to the header to say when the message arrived and where it
     52came from.  This allows one to reconstruct transmission problems
     53which may have affected the message along its route.
     54
     55{{{
     56  From: Christian Just <just@example.net>
     57}}}
     58
     59E-mail address and real name of the sender.
     60
     61{{{
     62  Reply-To: just@example.org
     63}}}
     64
     65The address to which any reply to this message should be sent.
     66This is used if the message is despatched from a computer which the
     67sender cannot use to read mail, for whatever reason.  Then he can use
     68this field to say where a reply should be sent.  In the absence of a
     69'''Reply-To:''' field, replies go to the address given in the '''From:''' field.
     70
     71{{{
     72  To: "Marcel Beck (Yet another Mailer-author)" <mbeck@example.com>
     73}}}
     74
     75The address of the recipient; additional names can be given,
     76separated by commas.  This field may contain simply the address
     77in the form name@domain or else it may be prefaced by an additional
     78comment, such as the recipient's name -- in this case, the address
     79must be enclosed in pointed brackets.
     80
     81{{{
     82  Date: Tue, 23 Dec 1997 23:28:30 +0200
     83}}}
     84
     85Date and time of despatch of the message.  The figure after the time
     86represents the timezone, expressed as the difference from Greenwich Mean
     87Time.  Here the first two digits show the hours, and the next two the
     88minutes.
     89
     90{{{
     91  Message-ID: <YAM7296.1549.122414920@zfn.uni-bremen.de>
     92}}}
     93
     94An unique identifier, created automatically on despatch.  Using
     95this it is possible unequivocally to cancel any particular message.
     96
     97{{{
     98  In-Reply-To: <YAM7296.263.121102896@mail.access.ch>
     99}}}
     100
     101A precise reference to the message being replied, such as its
     102Message-ID
     103
     104{{{
     105  X-Mailer: YAM 2.0beta4 - Amiga Mailer by Marcel Beck - http://yam.ch
     106}}}
     107
     108Name and Version of the sender's mail program.
     109
     110{{{
     111  Subject: Re: YAM2beta5
     112}}}
     113
     114This field should state concisely the topic of the message.  Giving
     115a clear and informative Subject is a mark of good style Netiquette.
     116
     117{{{
     118 Mime-Version: 1.0
     119 Content-Transfer-Encoding: quoted-printable
     120 Content-Type: text/plain; charset=iso-8859-1
     121}}}
     122
     123These fields indicate that the message is set out in MIME format.
     124In this example, it contains plain text in the ISO-Latin-1 character
     125set and characters which cannot be represented using 7 bits are encoded
     126as 'Quoted-printable'.
     127
     128[[=#FixProtocols]]
     129== Mail protocols
     130
     131YAM uses the Simple Mail Transfer Protocol (SMTP) in order to send
     132your mail to the SMTP server, which also uses SMTP to transmit your
     133mail across the whole world.  Incoming mail arrives at your Post Office
     134Protocol (POP) server, where it waits until YAM downloads it to your
     135computer, using the POP3 (POP version 3) protocols.  The messages which
     136YAM sends and receives conform to the conventions set out in RFC 822
     137and RFC 1521 (MIME).
     138
     139=== Outgoing mail
     140
     141If you want to send an e-mail message to anyone, YAM transfers the
     142message by SMTP to your local SMTP server.  This computer forwards the
     143message to the recipient's computer, generally also by SMTP.
     144
     145Why does YAM not deal directly with the recipient's server ?
     146Firstly, it would take quite a long time for your Amiga to get a
     147connection to one particular computer and then transmit the message.
     148Secondly, many computers are hard to find; it is much better to let the
     149mail server look for the address, instead of burdening your Amiga.
     150Thirdly, quite frequently the recipient's server will not be available
     151at the time you want to send the mail.  The SMTP server solves these
     152problems, holding back the message until the other computer is ready to
     153receive it.
     154
     155=== Incoming mail
     156
     157If someone sends you email, the other computer transfers it using
     158the SMTP protocol as far as your POP server.  This stores the message
     159in a sort of mailbox, where it remains until YAM collects it.  When you
     160look for new mail, YAM downloads the message to your Amiga using POP3.
     161
     162Why doesn't YAM use SMTP for incoming mail?  SMTP works best if
     163both computers are ready to receive messages.  Unless you run YAM and
     164your Amiga 24 hours a day and seven days a week, SMTP would not be
     165particularly suitable for you.
     166
     167[[=#FixMime]]
     168== What is MIME?
     169
     170MIME stands for ''Multipurpose Internet Mail Extensions''.  MIME serves
     171two main purposes: it allows one mail application to tell another what
     172sort of data is contained in a message, and it also provides
     173standardised rules by which mail applications can encode data, so that
     174it can be sent through the Internet mail system.
     175
     176=== MIME Encoding
     177
     178The Internet uses the SMTP protocol to move mail around.  SMTP is
     179limited to the US-ASCII character set.  This is a problem for people
     180who speak languages other than American English and so need accented
     181characters or non-American letters, or for people who want to use
     182special symbols like the bullet.  Even more difficult is the
     183transmission of binary files, as it is often the case with attachments.
     184MIME provides a way around this restriction by offering two
     185encodings: '''quoted-printable''' and '''base64'''.
     186
     187These encodings use US-ASCII character codes to represent any sort
     188of data you like, including special characters or even non-text data.
     189Quoted-printable is used for data that is mostly text, but has special
     190characters for very long lines.
     191
     192Quoted-printable looks just like regular text, except when a
     193special character is used -- the special character is replaced with
     194a "'''='''" (dash) and two more characters that represent the (hexadecimal)
     195character code of the special character.  Thus, a bullet in
     196quoted-printable looks like '''=95DA'''.
     197
     198No line in quoted-printable is allowed to be more than 76 characters
     199long.  If your mail has some line longer than 76 characters, the
     200quoted-printable encoding will break your line in two, and put a "'''='''"
     201at the end of the first line, to notify the mail reader at the other
     202end that the two lines are really supposed to be one.
     203
     204'''Base64''' encoding is another way to protect binary data from the
     205SMTP mail system.  However, Base64 makes no attempt to be readable,
     206and is more appropriate for non-text data.  It is equivalent to the
     207older UUencode, but more reliable in use.
     208
     209=== Content type
     210
     211The other important function of MIME is to allow mail programs to
     212exchange information about what kind of data is in a message (or part
     213of a message).  The primary mechanism used for this is the '''Content-Type:'''
     214header.  The main content types are:
     215
     216{{{
     217  text        readable text
     218  image       pictures and graphics
     219  audio       sound
     220  video       animations
     221  message     messages or parts of messages
     222  multipart   several different kinds of data in a single message
     223}}}
     224
     225The subtype gives additional information about the type of data:
     226
     227{{{
     228  text/plain   plain text
     229  text/html    text in HTML format
     230  image/gif    image in GIF format
     231  etc.
     232}}}
     233
     234By looking at the '''Content-Type:''' header, a mail program can select
     235the most suitable utility to display an attached file.
     236
     237[[=#FixPgp]]
     238== Encrypting with PGP
     239
     240In order to ensure that the e-mail cannot be read by anyone other
     241than the recipient, it is necessary to encrypt the transmission.  Is
     242this important?  Sometimes very much so!  It is not possible to say in
     243advance what route electronic mail will take through the Net and along
     244the way it is possible for someone to read your mail unauthorised,
     245admittedly with more trouble than one would normally bother to take.
     246In particular, encrypting e-mail is a wise precaution if you want to
     247send passwords, credit card numbers or some such over the Net.  Such
     248encrypted data is then often transmitted more safely than if sent by
     249normal letter post.  A simple, effective and widely used tool for this
     250sort of encryption is '''PGP''', short for '''Pretty Good Privacy'''.
     251
     252PGP was developed by Phil Zimmermann and employs the ''public key''
     253method.  Using this PGP program, one can be sure that the message is
     254the one actually written by the sender, and that only the intended
     255recipient can read it.  The so called ''public keys'' offer the highest
     256possible level of security.
     257
     258There are two kinds of key:
     259
     260  - One is a private key, used on your computer and never revealed
     261    elsewhere.
     262
     263  - The other sort is the public key.  You can make as many copies of
     264    this as you like, and send the copies to other users so that they
     265    can send you encrypted mail.
     266
     267You need both types of key, public and private, because they are inherently
     268connected together.  You can distribute your public key as
     269often as needed, but it will only work when matched up with its exact
     270counterpart.  Hence, both public and private keys are involved in
     271locking and (generally) unlocking information.
     272
     273PGP keys are used in two distinct ways:
     274
     275   1. Another person can encrypt information using your public key and
     276      send the encrypted file to you, to decipher with your private key.
     277
     278   2. You can encrypt information with your private key and send it
     279      safely over the Net.  Anyone in possession of your public key
     280      can read your communication.  The recipient can be sure that
     281      the communication is genuinely from you (your digital signature
     282      proves its authenticity) and that it has not been altered.
     283
     284PGP is obtainable as freeware and the International PGP homepage
     285is easy to find on the Internet at http://www.pgpi.org/
     286
     287__Related topics:__
     288
     289 * Installing PGP 2.6.x
     290 * Installing PGP 5.0i
     291
     292[[=#FixNetiquette]]
     293== E-mail netiquette
     294
     295- Keep your messages short and to the point.
     296
     297- Give the message a concise and meaningful '''Subject:''' header,
     298  so that it can easily be found again.
     299
     300- Put a signature at the end of the message.  This should contain
     301  your name and e-mail address and should not be longer than five
     302  lines.  Signatures often also give the postal address, telephone
     303  number, website and instructions about sending PGP messages.
     304
     305- Only write in block capitals if you want to give particular
     306  emphasis to a point.  *Stars* are also used for emphasis (YAM
     307  interprets this by using bold type).  Remember, block capitals
     308  are generally taken as equivalent to SHOUTING.
     309
     310- Set up YAM to use a line length of less than 80 characters and
     311  don't use any control characters.
     312
     313- Don't use non-ASCII characters unless you are sure that the
     314  recipient's software interprets them correctly.
     315
     316- It is regarded as extremely impolite to forward a private message
     317  to a mailing list without the permission of the original sender.
     318
     319- Abbreviations and ''TLAs'' (Three Letter Acronyms) can be useful
     320  provided that they don't make the message unintelligible.
     321  The following are often used:
     322
     323            IMHO   (in my humble opinion)
     324            BTW    (by the way)
     325            FYI    (for your information)
     326            AFAIK  (as far as I know)
     327            ASAP   (as soon as possible)
     328            CU     (see you)
     329
     330- Use the ;-) smiley (winky?) to denote a touch of irony which could
     331  otherwise easily be misinterpreted.
     332
     333- Be tolerant of people's failings, e.g. in spelling, grammar, expression
     334  or familiarity with e-mail.
     335
     336- If you join a mailing list, read the messages for a while to get a
     337  feel of the general style, what questions are asked and what is
     338  not suitable.
     339
     340- Study the ''FAQs'' (lists of Frequently Asked Questions).  It is
     341  annoying for the members of a group if the same questions are
     342  being asked repeatedly.
     343
     344- If someone posts a message which is "off-topic", (i.e. it does not
     345  belong in the mailing list), reply privately and NOT in the list.
     346
     347- If you quote another message, then cut all the bits which are not
     348  relevant to your answer.  No-one wants to read the same message
     349  three or four times, especially when all that is added is "Yes, me
     350  too".
     351
     352- Resist the temptation to flame in the mailing list.  ("Flame" =
     353  write abusively, generally when provoked by idiocy.)  Remember that
     354  the list is public and meant for constructive discussion.  Do as
     355  you would be done by!
     356
     357- If you are replying to a message coming from a mailing list, think
     358  carefully whether to send it direct to the sender or to the list,
     359  and check that the ''To:'' address is correct.  It can be very
     360  irritating when a letter addressed to a particular person appears
     361  on the list, unintentionally.
     362
     363- When replying to a message coming from a mailing list, it is usually
     364  a good idea to mention the person who wrote that message as part of
     365  your welcome phrase, to avoid confusion.