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 in a role being used.
 139
 140 <LI><EM>smtp-server</EM> specified on the command line.
 141
 142 <LI><EM>sendmail-path</EM> in the user's <CODE>.pinerc</CODE> file.
 143
 144 <LI><EM>smtp-server</EM> in the user's <CODE>.pinerc</CODE> file.
 145
 146 <LI><EM>sendmail-path</EM> in <CODE>/usr/local/lib/pine.conf</CODE>
 147
 148 <LI><EM>smtp-server</EM> in <CODE>/usr/local/pine.conf</CODE>
 149
 150 <LI><CODE>DF_SENDMAIL_PATH</CODE> defined at compile time.
 151
 152 <LI><CODE>SENDMAIL</CODE> and <CODE>SENDMAILFLAGS</CODE> defined at
 153 compile time.
 154
 155 </OL><P>
 156
 157 If the <EM>sendmail-path</EM> form is used, a child process is forked,
 158 and the specified command is executed with the message passed on standard
 159 input.  Standard output is then passed back and displayed for the user.
 160 <EM>NOTE: The program MUST read the message to be posted on standard
 161 input, AND operate in the style of sendmail's "-t" option. This
 162 method is not recommended unless there are special reasons you
 163 want to do this. </EM><P>
 164
 165 If an <EM>smtp-server</EM> is specified,
 166 <EM>Alpine</EM> operates as an SMTP client.  SMTP stands for <EM>Simple Mail
 167 Transfer Protocol</EM>; it specifies the rules by which computers on the
 168 Internet pass email to one another.  In this case, <EM>Alpine</EM> passes outgoing
 169 email messages to a designated SMTP server instead of to a mail transfer
 170 program on the local machine.  A program on the server then takes care of
 171 delivering the message.  To make <EM>Alpine</EM> operate as an SMTP client, the
 172 <A HREF="config.html#smtp-server"><EM>smtp-server</EM></A> variable
 173 must be set to the IP address or
 174 host name of the SMTP server within your organization.  This variable accepts a
 175 comma separated list of servers, so you can specify multiple alternate SMTP servers.
 176 <EM>PC-Alpine</EM> only runs as an SMTP client so the <EM>smtp-server</EM>
 177 option is mandatory.  <P>
 178
 179 For UNIX <EM>Alpine</EM>,
 180 if neither <EM>smtp-server</EM> or <EM>sendmail-path</EM> is set,
 181 the default <CODE>sendmail</CODE> program is
 182 invoked with the "<CODE>-bs -odb -oem</CODE>" flags, and the message
 183 is sent using the SMTP protocol.
 184 <P>
 185
 186 <HR>
 187
 188 <H2><A NAME="IMAP">Internet Message Access Protocol (IMAP)</A></H2>
 189
 190 IMAP is a remote access protocol for message stores. <EM>Alpine</EM> uses IMAP to get
 191 at messages and folders which reside on remote machines. With IMAP,
 192 messages are kept on the server.  An IMAP client (such as <EM>Alpine</EM>) can
 193 request specific messages, headers, message structures, message parts, etc.  The client
 194 can also issue commands which delete messages from folders on the server.
 195 IMAP's closest kin is POP, the Post Office Protocol, which works by
 196 transferring an entire mailbox to the client where all the mail is kept.
 197 For a comparison of IMAP and POP, see the paper "<A
 198 HREF="http://www.imap.org/imap.vs.pop.brief.html">Comparing Two Approaches
 199 to Remote Mailbox Access: IMAP vs. POP</A>" by Terry Gray.  A more
 200 detailed exploration of message access may be found in the paper "<A
 201 HREF="http://www.imap.org/imap.vs.pop.html"> Message Access Paradigms and
 202 Protocols</A>."
 203 <P>
 204
 205 IMAP Features:
 206
 207 <UL>
 208
 209 <LI> Allows access to mail folders from more than one client computer.
 210
 211 <LI> Works well over low-bandwidth lines because information is sent in
 212 small pieces as needed by the user.  For example, only header information
 213 is sent to build index lists, and if someone sends a large audio file via
 214 MIME, you can choose when (or if) you want to get that part of the
 215 message.
 216
 217 <LI> Email can be delivered and stored on a well-maintained and reliable
 218 server which is "always-up".
 219
 220 <LI> Folders can be accessed and manipulated from anywhere on the
 221 Internet.
 222
 223 <LI> Users can get to messages stored in different folders within the same
 224 <EM>Alpine</EM> session.
 225
 226 <LI> Allows use of IMAP server for searching and parsing.
 227
 228 <LI> The latest revision of IMAP (IMAP4) also provides for disconnected
 229 operation, including resynchronization of message state between mail
 230 servers and message caches on clients.  <EM>Alpine</EM> does not support this
 231 capability, however.
 232
 233 </UL>
 234
 235 IMAP4rev1 is described in <A
 236 HREF="ftp://ftp.isi.edu/in-notes/rfc3501.txt">RFC 3501</A>.  Further
 237 information about IMAP may be obtained from the University of Washington's
 238 <A HREF="http://www.washington.edu/imap/">IMAP Information Center</A>.<P>
 239
 240 <EM>Alpine</EM> is an IMAP4rev1 client.
 241 <P>
 242
 243 <HR>
 244
 245 <H2><A NAME="MIME">Multipurpose Internet Mail Extensions (MIME)</A></H2>
 246
 247 MIME is a way of encoding a multipart message structure into a standard
 248 Internet email message.  The parts may be nested and may be of seven
 249 different types:  Text, Audio, Image, Video, Message, Application and
 250 Multipart (nested).  The MIME specification allows email programs such as
 251 <EM>Alpine</EM> to reliably and simply exchange binary data (images, spreadsheets,
 252 etc.). MIME includes support for international character sets, tagging each
 253 part of a message with the character set it is written in, and providing
 254 7-bit encoding of 8-bit character sets.  <P>
 255
 256 The MIME standard was officially published in June of 1992 as <A
 257 HREF="ftp://ftp.isi.edu/in-notes/rfc1341.txt">RFC 1341</A> and subsequently
 258 revised in <A HREF="ftp://ftp.isi.edu/in-notes/rfc2045.txt">RFC 2045</A>
 259 when it became a full Internet Standard.  <EM>Pine</EM> 3.0 was one of the first
 260 email programs to Implement MIME.  Now, there are dozens of commercial and
 261 freely available MIME-capable email programs. In addition, MIME is being
 262 added to newsreaders so MIME messages can be posted and read in USENET
 263 newsgroups.  <P>
 264
 265 The MIME standard also includes support for non-ASCII text in message
 266 headers through the extensions described in <A
 267 HREF="ftp://ftp.isi.edu/in-notes/rfc1342.txt">RFC 1342</A> and subsequently
 268 revised in <A HREF="ftp://ftp.isi.edu/in-notes/rfc2047.txt">RFC 2047</A>.  <P>
 269
 270 An actual MIME message looks something like this:
 271
 272 <PRE>
 273 Date: Tue, 12 Mar 1996 15:39:35 -0800 (PST)
 274 From: David L Miller &lt;dlm@cac.washington.edu&gt;
 275 To: David L Miller &lt;dlm@cac.washington.edu&gt;
 276 Subject: =?iso-8859-1?Q?Test_MIME_message_with_RFC-1522_headers_=28=E1?=    =?iso-8859-1?Q?=E2=E3=29?=
 277 Message-Id: &lt;Pine.ULT.3.92.960312150851.21583I-101000@shiva2.cac.washington.edu&gt;
 278 Mime-Version: 1.0
 279 Content-Type: MULTIPART/MIXED; BOUNDARY="0-1737669234-826673975=:21583"
 280 Content-Id: &lt;Pine.ULT.3.92.960312153928.21583O@shiva2.cac.washington.edu&gt;
 281
 282   This message is in MIME format.  The first part should be readable text,
 283   while the remaining parts are likely unreadable without MIME-aware tools.
 284   Send mail to mime@docserver.cac.washington.edu for more info.
 285
 286 --0-1737669234-826673975=:21583
 287 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
 288 Content-ID: &lt;Pine.ULT.3.92.960312153104.21583L@shiva2.cac.washington.edu&gt;
 289
 290 The text of the message would go here. It is readable if
 291 one doesn't mind wading around a little bit of the MIME
 292 formatting. After this is a binary file in base 64
 293 encoding.
 294
 295 |\ |  |\/|  David L. Miller    dlm@cac.washington.edu  (206) 685-6240
 296 |/ |_ |  |  Software Engineer, Pine Development Team   (206) 685-4045 (FAX)
 297 University of Washington, Networks & Distributed Computing, JE-20
 298 4545 15th Ave NE, Seattle WA 98105, USA
 299
 300 --0-1737669234-826673975=:21583
 301 Content-Type: APPLICATION/ZIP; NAME="test.zip"
 302 Content-Transfer-Encoding: BASE64
 303 Content-ID: &lt;Pine.ULT.3.92.960312153638.21583N@shiva2.cac.washington.edu&gt;
 304 Content-Description: Test Attachment
 305
 306 UEsDBBQAAAAIAGh8bCBbZKT4ygIAAHgFAAAEAAAAdGVzdIVUX2vbMBB/16c4
 307 9rSBNyjsYX1UHSUROLInycv2qNhKI5ZYxlLa5dvvpDRLw6CFgJF09/t3Rxo3
 308 WDBDD43rPJjJQpxMbw9m+h3AbyHuLLSDe7JTcPGUbtYm7NzwGP3wBYQnnT8c
 309 7NQ5s4djsC8t4QbmYE6wsfjpLTy7uPPHCOPk/ATPk4vRDmS008GF4PzwPich
 310 zY3m4LfxOQlPNy4GcEO3P/a2h2j/xGyp9ONpco+7CHf33+4/393ff4XNibzL
 311 c1UVfXJXQIdIBRx877b4TYy9C3Fym2NEyzsX/pNDet8dD3aIJiagLbo2wwnG
 312 4zT6cK66ZLK1NhH9J4tcZQEy7OxkNyd4nMwQbV9glP7JZb87E3O32fgnm7We
 313 XQ8+us4SM47WTCkgMPt9enc2ZAW5c+Pj7o32l0IXXk/r8pSRE3A4jqOfIqqF
 314 G+PFlSdRDOaQduXNESTwtDcYfJ8191gWXUjYmOJ43Oxdh11JTzRuSPcY37+B
 315 vNqmf0O5RB1G27mt64rLCp4X8pW1L6BvxunCeYHNk3F7s9lb+GAwyvAhOyNE
 316 Lxm0gv9gUnH9C+o5rKlacrHQtYAZV2VF+UoBrSp8kJIKzZkqgP1sJFMKagl8
 317 1VSczQqy5noJki2onIGuQS+5AlXPNfaxArgoq3aGwJDq6lZDxVdcU82RKMG/
 318 4JArTVKzYrJc4pE+8CoJpGIGc65FIp8jO4WGSs3LtqISmlY2tUKyVMUFETWw
 319 H0xoUMvE8KbXB4aC6EPFzrDiF6iGlZxWBeFixiUrdXJb1kKx7y2C4hPM6Iou
 320 WI4hdVyO6yXVqkZqiXmottLJ9lzWK1LVKttqk8oZ1TS1NrJGS5jqeslQI0aK
 321 ieCvzNlgNZJqiccCc5WafLxmKdii4gsmSvYpISkteamzkRwXJiG5SoUpcERK
 322 8xIE8QQ7o+eh5WAUy1qYRP8rioip/maI+OfyF1BLAQIUAxQAAAAIAGh8bCBb
 323 ZKT4ygIAAHgFAAAEAAAAAAAAAAEAAACkgQAAAAB0ZXN0UEsFBgAAAAABAAEA
 324 MgAAAOwCAAAAAA==
 325 --0-1737669234-826673975=:21583--
 326
 327 </PRE>
 328
 329 For details about <EM>Alpine</EM>'s implementation of MIME, see the two MIME sections
 330 "<A HREF="low-level.html#MIME-read">MIME:  Reading a Message</A>" and
 331 "<A HREF="low-level.html#MIME-send">MIME:  Sending a Message</A>" later
 332 in this document.  <P>
 333
 334 <HR>
 335
 336 <H2><A NAME="collections">Folder Collections</A></H2>
 337
 338 Folder Collections are <EM>Alpine</EM>'s way of dealing with more than a single group
 339 of folders. <P>
 340
 341 For a more complete description of Folder Collections, see the section on
 342 "<A HREF="config-notes.html#collections">Syntax for Collections</A>."  <P>
 343
 344 The <EM>Alpine</EM> distribution is designed to require as little configuration and
 345 effort at compile time as possible.  Still, there are some <EM>Alpine</EM> behaviors
 346 which are set at the time you compile <EM>Alpine</EM>.  For each of these, there is a
 347 reasonable (our opinion) default built into the code, so most systems
 348 administrators will have no need for these steps.  <P>
 349
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