doc/tech-notes/background.html

   1 <HTML><HEAD><TITLE>Alpine Technical Notes: Background Details</TITLE></HEAD><BODY>
   2 <H1>Background Details</H1>
   3
   4 <H2><A NAME="DNS">Domain Names</A></H2>
   5
   6 <BR><P>
   7
   8 Domain names are used to uniquely name each host on the Internet.  A
   9 domain name has a number of parts separated by periods.  Each label
  10 represents a level in the hierarchy.  An example of a name is:
  11
  12 <BLOCKQUOTE><CODE>
  13 olive.cac.washington.edu
  14 </CODE></BLOCKQUOTE>
  15
  16 In this domain name the top-level label is <EM>edu</EM>, indicating it is
  17 at an educational institution, the second-level label is
  18 <EM>washington</EM>, indicating the University of Washington.
  19 <EM>cac</EM> is a specific department within the University of Washington,
  20 and <EM>olive</EM> is the host name.  The top-level names are assigned by
  21 Internet organizations, and other names are assigned at the appropriate
  22 level.  The Domain Name Service, DNS, is the distributed database used to
  23 look up these names.  <P>
  24
  25 <EM>Alpine</EM> relies on domain names in multiple places.
  26 A domain name is embedded
  27 into the message-id line generated for each piece of email.  A domain name
  28 is needed to contact an IMAP server to get access to remote INBOXes and
  29 folders.  Most importantly, domain names are needed to construct the From:
  30 line of your outgoing messages so that people on the Internet will be able
  31 to get email back to you.  <P>
  32
  33 On UNIX systems, you can set the domain via the <A
  34 HREF="config.html#user-domain"><EM>user-domain</EM></A>
  35 variable in the <EM>Alpine</EM> configuration file, or rely on the file
  36 <CODE>/etc/hosts</CODE> which usually sets the name of the local host.
  37 While <EM>Alpine</EM> can often deliver email without the domain name
  38 being properly
  39 configured, it is best to have this set correctly.  Problems can usually be
  40 solved by adjusting the system's entry in the <CODE>/etc/hosts</CODE>
  41 file.  The fully-qualified name should be listed before any abbreviations.
  42 For example,
  43
  44 <BLOCKQUOTE><CODE>
  45 128.95.112.99   olive.cac.washington.edu   olive
  46 </CODE></BLOCKQUOTE>
  47
  48 is preferred over
  49
  50 <BLOCKQUOTE><CODE>
  51 128.95.112.99   olive   olive.cac.washington.edu
  52 </CODE></BLOCKQUOTE>
  53 <P>
  54
  55 On PCs, the task of configuring the domain name is a bit different.  Often
  56 times PCs do not have domain names-they have <EM>IP addresses</EM>.  IP
  57 addresses are the numbers which uniquely identify a computer on the
  58 network.  The way you configure your IP address depends on the networking
  59 software which you use on the PC.  You can refer to the documentation
  60 which came with your networking software or see the <A
  61 HREF="installation.html#install-pc">PC specific installation notes</A> for
  62 help configuring the IP address with your network software.  <P>
  63
  64 With PCs, it is vital that users set the variable <A
  65 HREF="config.html#user-domain"><EM>user-domain</EM></A> in the <EM>Alpine</EM>
  66 configuration file (<CODE>PINERC</CODE>).  <P>
  67
  68 Details on configuring <EM>Alpine</EM> with correct domain names can be
  69 found in the <A HREF="config-notes.html#domain">Domain Settings</A>
  70 section of this document.  <P>
  71
  72 <HR>
  73
  74 <H2><A NAME="rfc2822">RFC 2822 Compliance</A></H2>
  75
  76 <EM>Alpine</EM> tries to adhere
  77 to <A HREF="ftp://ftp.isi.edu/in-notes/rfc2822.txt">RFC 2822</A>
  78 fairly strictly.  <P>
  79
  80 As far as outgoing email is concerned, <EM>Alpine</EM> fully-qualifies addresses
  81 whenever possible.  They are even displayed in fully-qualified form on the
  82 terminal as the user composes a message.  This makes addresses more clear
  83 and gives a hint to the user that the network extends beyond the local
  84 organization.
  85 <EM>Alpine</EM> implements fully-qualified domain names by tacking on
  86 the local domain to all unqualified addresses which a user types in.  Any
  87 address which does not contain an "@" is considered unqualified.  <P>
  88
  89 The format for addresses allows for spaces and special characters in
  90 the full name of an address.  For this reason, commas are required to
  91 separate addresses.  If any special characters as defined in RFC 2822
  92 appear in the full name, quotes are required around the address.  <EM>Alpine</EM>
  93 will insert the quotes automatically if needed.  The common cases where this happens
  94 are with periods after initials and parentheses.  <P>
  95
  96 <EM>Alpine</EM> expects dates to be in the standard RFC 822 format
  97 which is something like:
  98
  99 <PRE>
 100         [www, ] dd mmm yy hh:mm[:ss] [timezone]
 101 </PRE>
 102
 103 It will attempt to parse dates that are not in this format.  When an
 104 unparsable date is encountered it is shown as question marks
 105 in the FOLDER INDEX screen.  <P>
 106
 107 <HR>
 108
 109 <H2><A NAME="SMTP">SMTP and Sendmail</A></H2>
 110
 111 <EM>Alpine</EM> is a <EM>user agent</EM> not a <EM>message transfer agent</EM> (MTA). In
 112 plain English, that means <EM>Alpine</EM> does not know how to interact with other
 113 computers on the Internet to deliver or receive email.  What <EM>Alpine</EM> does
 114 know how to do is help users read, organize and create email.  The "dirty
 115 work" of delivering and accepting email is handled by other programs.  <P>
 116
 117 All outgoing email is delivered to an SMTP server
 118 or to a mail transfer agent.
 119 A common mail transfer agent is <CODE>sendmail</CODE>.
 120 The usual method of delivery used by <EM>Alpine</EM> is to use either a
 121 local or a remote SMTP server.
 122
 123 <P> The selection of which MTA to use depends on the settings of
 124 <A HREF="config.html#smtp-server"><EM>smtp-server</EM></A>,
 125 <A HREF="config.html#sendmail-path"><EM>sendmail-path</EM></A>,
 126 and compile-time options.
 127 The first MTA specified in the following list is used:
 128
 129 <OL>
 130
 131 <LI><EM>sendmail-path</EM> in
 132 <CODE>/usr/local/lib/pine.conf.fixed</CODE>
 133
 134 <LI><EM>smtp-server</EM> in <CODE>/usr/local/pine.conf.fixed</CODE>
 135
 136 <LI><EM>sendmail-path</EM> specified on the command line.
 137
 138 <LI><EM>smtp-server</EM> specified on the command line.
 139
 140 <LI><EM>sendmail-path</EM> in the user's <CODE>.pinerc</CODE> file.
 141
 142 <LI><EM>smtp-server</EM> in the user's <CODE>.pinerc</CODE> file.
 143
 144 <LI><EM>sendmail-path</EM> in <CODE>/usr/local/lib/pine.conf</CODE>
 145
 146 <LI><EM>smtp-server</EM> in <CODE>/usr/local/pine.conf</CODE>
 147
 148 <LI><CODE>DF_SENDMAIL_PATH</CODE> defined at compile time.
 149
 150 <LI><CODE>SENDMAIL</CODE> and <CODE>SENDMAILFLAGS</CODE> defined at
 151 compile time.
 152
 153 </OL><P>
 154
 155 If the <EM>sendmail-path</EM> form is used, a child process is forked,
 156 and the specified command is executed with the message passed on standard
 157 input.  Standard output is then passed back and displayed for the user.
 158 <EM>NOTE: The program MUST read the message to be posted on standard
 159 input, AND operate in the style of sendmail's "-t" option. This
 160 method is not recommended unless there are special reasons you
 161 want to do this. </EM><P>
 162
 163 If an <EM>smtp-server</EM> is specified,
 164 <EM>Alpine</EM> operates as an SMTP client.  SMTP stands for <EM>Simple Mail
 165 Transfer Protocol</EM>; it specifies the rules by which computers on the
 166 Internet pass email to one another.  In this case, <EM>Alpine</EM> passes outgoing
 167 email messages to a designated SMTP server instead of to a mail transfer
 168 program on the local machine.  A program on the server then takes care of
 169 delivering the message.  To make <EM>Alpine</EM> operate as an SMTP client, the
 170 <A HREF="config.html#smtp-server"><EM>smtp-server</EM></A> variable
 171 must be set to the IP address or
 172 host name of the SMTP server within your organization.  This variable accepts a
 173 comma separated list of servers, so you can specify multiple alternate SMTP servers.
 174 <EM>PC-Alpine</EM> only runs as an SMTP client so the <EM>smtp-server</EM>
 175 option is mandatory.  <P>
 176
 177 For UNIX <EM>Alpine</EM>,
 178 if neither <EM>smtp-server</EM> or <EM>sendmail-path</EM> is set,
 179 the default <CODE>sendmail</CODE> program is
 180 invoked with the "<CODE>-bs -odb -oem</CODE>" flags, and the message
 181 is sent using the SMTP protocol.
 182 <P>
 183
 184 <HR>
 185
 186 <H2><A NAME="IMAP">Internet Message Access Protocol (IMAP)</A></H2>
 187
 188 IMAP is a remote access protocol for message stores. <EM>Alpine</EM> uses IMAP to get
 189 at messages and folders which reside on remote machines. With IMAP,
 190 messages are kept on the server.  An IMAP client (such as <EM>Alpine</EM>) can
 191 request specific messages, headers, message structures, message parts, etc.  The client
 192 can also issue commands which delete messages from folders on the server.
 193 IMAP's closest kin is POP, the Post Office Protocol, which works by
 194 transferring an entire mailbox to the client where all the mail is kept.
 195 For a comparison of IMAP and POP, see the paper "<A
 196 HREF="http://www.imap.org/imap.vs.pop.brief.html">Comparing Two Approaches
 197 to Remote Mailbox Access: IMAP vs. POP</A>" by Terry Gray.  A more
 198 detailed exploration of message access may be found in the paper "<A
 199 HREF="http://www.imap.org/imap.vs.pop.html"> Message Access Paradigms and
 200 Protocols</A>."
 201 <P>
 202
 203 IMAP Features:
 204
 205 <UL>
 206
 207 <LI> Allows access to mail folders from more than one client computer.
 208
 209 <LI> Works well over low-bandwidth lines because information is sent in
 210 small pieces as needed by the user.  For example, only header information
 211 is sent to build index lists, and if someone sends a large audio file via
 212 MIME, you can choose when (or if) you want to get that part of the
 213 message.
 214
 215 <LI> Email can be delivered and stored on a well-maintained and reliable
 216 server which is "always-up".
 217
 218 <LI> Folders can be accessed and manipulated from anywhere on the
 219 Internet.
 220
 221 <LI> Users can get to messages stored in different folders within the same
 222 <EM>Alpine</EM> session.
 223
 224 <LI> Allows use of IMAP server for searching and parsing.
 225
 226 <LI> The latest revision of IMAP (IMAP4) also provides for disconnected
 227 operation, including resynchronization of message state between mail
 228 servers and message caches on clients.  <EM>Alpine</EM> does not support this
 229 capability, however.
 230
 231 </UL>
 232
 233 IMAP4rev1 is described in <A
 234 HREF="ftp://ftp.isi.edu/in-notes/rfc3501.txt">RFC 3501</A>.  Further
 235 information about IMAP may be obtained from the University of Washington's
 236 <A HREF="http://www.washington.edu/imap/">IMAP Information Center</A>.<P>
 237
 238 <EM>Alpine</EM> is an IMAP4rev1 client.
 239 <P>
 240
 241 <HR>
 242
 243 <H2><A NAME="MIME">Multipurpose Internet Mail Extensions (MIME)</A></H2>
 244
 245 MIME is a way of encoding a multipart message structure into a standard
 246 Internet email message.  The parts may be nested and may be of seven
 247 different types:  Text, Audio, Image, Video, Message, Application and
 248 Multipart (nested).  The MIME specification allows email programs such as
 249 <EM>Alpine</EM> to reliably and simply exchange binary data (images, spreadsheets,
 250 etc.). MIME includes support for international character sets, tagging each
 251 part of a message with the character set it is written in, and providing
 252 7-bit encoding of 8-bit character sets.  <P>
 253
 254 The MIME standard was officially published in June of 1992 as <A
 255 HREF="ftp://ftp.isi.edu/in-notes/rfc1341.txt">RFC 1341</A> and subsequently
 256 revised in <A HREF="ftp://ftp.isi.edu/in-notes/rfc2045.txt">RFC 2045</A>
 257 when it became a full Internet Standard.  <EM>Pine</EM> 3.0 was one of the first
 258 email programs to Implement MIME.  Now, there are dozens of commercial and
 259 freely available MIME-capable email programs. In addition, MIME is being
 260 added to newsreaders so MIME messages can be posted and read in USENET
 261 newsgroups.  <P>
 262
 263 The MIME standard also includes support for non-ASCII text in message
 264 headers through the extensions described in <A
 265 HREF="ftp://ftp.isi.edu/in-notes/rfc1342.txt">RFC 1342</A> and subsequently
 266 revised in <A HREF="ftp://ftp.isi.edu/in-notes/rfc2047.txt">RFC 2047</A>.  <P>
 267
 268 An actual MIME message looks something like this:
 269
 270 <PRE>
 271 Date: Tue, 12 Mar 1996 15:39:35 -0800 (PST)
 272 From: David L Miller &lt;dlm@cac.washington.edu&gt;
 273 To: David L Miller &lt;dlm@cac.washington.edu&gt;
 274 Subject: =?iso-8859-1?Q?Test_MIME_message_with_RFC-1522_headers_=28=E1?=    =?iso-8859-1?Q?=E2=E3=29?=
 275 Message-Id: &lt;Pine.ULT.3.92.960312150851.21583I-101000@shiva2.cac.washington.edu&gt;
 276 Mime-Version: 1.0
 277 Content-Type: MULTIPART/MIXED; BOUNDARY="0-1737669234-826673975=:21583"
 278 Content-Id: &lt;Pine.ULT.3.92.960312153928.21583O@shiva2.cac.washington.edu&gt;
 279
 280   This message is in MIME format.  The first part should be readable text,
 281   while the remaining parts are likely unreadable without MIME-aware tools.
 282   Send mail to mime@docserver.cac.washington.edu for more info.
 283
 284 --0-1737669234-826673975=:21583
 285 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
 286 Content-ID: &lt;Pine.ULT.3.92.960312153104.21583L@shiva2.cac.washington.edu&gt;
 287
 288 The text of the message would go here. It is readable if
 289 one doesn't mind wading around a little bit of the MIME
 290 formatting. After this is a binary file in base 64
 291 encoding.
 292
 293 |\ |  |\/|  David L. Miller    dlm@cac.washington.edu  (206) 685-6240
 294 |/ |_ |  |  Software Engineer, Pine Development Team   (206) 685-4045 (FAX)
 295 University of Washington, Networks & Distributed Computing, JE-20
 296 4545 15th Ave NE, Seattle WA 98105, USA
 297
 298 --0-1737669234-826673975=:21583
 299 Content-Type: APPLICATION/ZIP; NAME="test.zip"
 300 Content-Transfer-Encoding: BASE64
 301 Content-ID: &lt;Pine.ULT.3.92.960312153638.21583N@shiva2.cac.washington.edu&gt;
 302 Content-Description: Test Attachment
 303
 304 UEsDBBQAAAAIAGh8bCBbZKT4ygIAAHgFAAAEAAAAdGVzdIVUX2vbMBB/16c4
 305 9rSBNyjsYX1UHSUROLInycv2qNhKI5ZYxlLa5dvvpDRLw6CFgJF09/t3Rxo3
 306 WDBDD43rPJjJQpxMbw9m+h3AbyHuLLSDe7JTcPGUbtYm7NzwGP3wBYQnnT8c
 307 7NQ5s4djsC8t4QbmYE6wsfjpLTy7uPPHCOPk/ATPk4vRDmS008GF4PzwPich
 308 zY3m4LfxOQlPNy4GcEO3P/a2h2j/xGyp9ONpco+7CHf33+4/393ff4XNibzL
 309 c1UVfXJXQIdIBRx877b4TYy9C3Fym2NEyzsX/pNDet8dD3aIJiagLbo2wwnG
 310 4zT6cK66ZLK1NhH9J4tcZQEy7OxkNyd4nMwQbV9glP7JZb87E3O32fgnm7We
 311 XQ8+us4SM47WTCkgMPt9enc2ZAW5c+Pj7o32l0IXXk/r8pSRE3A4jqOfIqqF
 312 G+PFlSdRDOaQduXNESTwtDcYfJ8191gWXUjYmOJ43Oxdh11JTzRuSPcY37+B
 313 vNqmf0O5RB1G27mt64rLCp4X8pW1L6BvxunCeYHNk3F7s9lb+GAwyvAhOyNE
 314 Lxm0gv9gUnH9C+o5rKlacrHQtYAZV2VF+UoBrSp8kJIKzZkqgP1sJFMKagl8
 315 1VSczQqy5noJki2onIGuQS+5AlXPNfaxArgoq3aGwJDq6lZDxVdcU82RKMG/
 316 4JArTVKzYrJc4pE+8CoJpGIGc65FIp8jO4WGSs3LtqISmlY2tUKyVMUFETWw
 317 H0xoUMvE8KbXB4aC6EPFzrDiF6iGlZxWBeFixiUrdXJb1kKx7y2C4hPM6Iou
 318 WI4hdVyO6yXVqkZqiXmottLJ9lzWK1LVKttqk8oZ1TS1NrJGS5jqeslQI0aK
 319 ieCvzNlgNZJqiccCc5WafLxmKdii4gsmSvYpISkteamzkRwXJiG5SoUpcERK
 320 8xIE8QQ7o+eh5WAUy1qYRP8rioip/maI+OfyF1BLAQIUAxQAAAAIAGh8bCBb
 321 ZKT4ygIAAHgFAAAEAAAAAAAAAAEAAACkgQAAAAB0ZXN0UEsFBgAAAAABAAEA
 322 MgAAAOwCAAAAAA==
 323 --0-1737669234-826673975=:21583--
 324
 325 </PRE>
 326
 327 For details about <EM>Alpine</EM>'s implementation of MIME, see the two MIME sections
 328 "<A HREF="low-level.html#MIME-read">MIME:  Reading a Message</A>" and
 329 "<A HREF="low-level.html#MIME-send">MIME:  Sending a Message</A>" later
 330 in this document.  <P>
 331
 332 <HR>
 333
 334 <H2><A NAME="collections">Folder Collections</A></H2>
 335
 336 Folder Collections are <EM>Alpine</EM>'s way of dealing with more than a single group
 337 of folders. <P>
 338
 339 For a more complete description of Folder Collections, see the section on
 340 "<A HREF="config-notes.html#collections">Syntax for Collections</A>."  <P>
 341
 342 The <EM>Alpine</EM> distribution is designed to require as little configuration and
 343 effort at compile time as possible.  Still, there are some <EM>Alpine</EM> behaviors
 344 which are set at the time you compile <EM>Alpine</EM>.  For each of these, there is a
 345 reasonable (our opinion) default built into the code, so most systems
 346 administrators will have no need for these steps.  <P>
 347
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