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


Ignore:
Timestamp:
Oct 21, 2013 10:06:07 PM (13 months ago)
Author:
AmigaPhil
Comment:

--

Legend:

Unmodified
Added
Removed
Modified
  • fr:Documentation/What is e-mail

    v4 v5  
    1 [[TranslatedPages(revision=1)]]\\ 
     1[[TranslatedPages(revision=10,outdated=THIS PAGE NEEDS TRANSLATION)]]\\ 
    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.