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  • pg 1
									Electronic Mail
Familiar to most of us
 What are the functions we expect?
  – Outgoing mail
     • Compose
     • send
          – compress
          – encrypt
  – Incoming Mail
     •   read
     •   forward
     •   repl
     •   store (retain) (and organize into folders, search, …)
     •   discard
     •   others????
The X.400 Functional Model

User   UA              P2                         UA           User

         P3                         MS    (ex: POP or IMAP)
         (ex: SMTP)

                                     P3                  AU
                                     (ex: SMTP)
              MTA                                               Other
        MTS           (ex: SMTP)
       MHS                                                    Services
 User to the User Agent
   – local issue, no need to standardize
 P1: Message Transfer Agent interaction
   – concerned with routing and protection
   – not interested in message format or content
 P2: User Agent to User Agent
   – common packaging and interpretation of labels
 P3: Between the UA or MS and the MTA
   – hand over the message for safe delivery
 AU = Access Unit; PDAU = Physical Delivery Access Unit
   – non standard delivery, such as e-mail to fax, e-
     mail to postal mail, etc.
Sending a message
 Use DNS to get IP address of the
  destination mail server
 Establish a TCP/IP connection to the server
 (Optional) establish a SSL connection to the
 Send header and message

   Ref: http://docs.iplanet.com/docs/manuals/messaging/nms41/ag/routing.htm#1017549
Routing a message
1. Queries the Directory Server to determine whether the recipient is local or
2. If the recipient is local, delivers the message, typically placing it in the
   message store. Otherwise, proceeds to step 3.
3. If the recipient is remote:
    a. Queries DNS to find the MX (mail exchange) servers for the domain.
    b. Queries DNS to find the IP address of the remote messaging server.
    c. Establishes a TCP/IP connection to the remote messaging server.
    d. (Optional) Establishes an SSL connection to the remote messaging
    e. Sends the message to the remote messaging server (SMTP-Deliver).

      Ref: http://docs.iplanet.com/docs/manuals/messaging/nms41/ag/routing.htm#1017549
Retrieving a message
To retrieve a message, the client must know the IP address of the
messaging server, establish a connection to the server, then retrieve the
message using one of the retrieval protocols: POP, IMAP, or HTTP. The
following summarizes the steps the client takes to retrieve a message.

        1.Queries DNS to find the IP address of the server.

        2.Establishes a TCP/IP connection to the server.

        3.(Optional) Establishes an SSL connection to the server.

         4.Establishes a POP3, IMAP4, or HTTP connection to the server
to retrieve the message.

     Ref: http://docs.iplanet.com/docs/manuals/messaging/nms41/ag/routing.htm#1017549
 User Interface
  – mail program environment
     • hints and clues about what to do next
     • reminders of folder names, aliases
  – set of individual commands to execute as
     • easy to incorporate mail functions into other
 Knowing about success or failure
     • failure can occur at any of several places in the mail
       delivery system
Mail Interface
 Netscape/Mozilla
 Outlook
 unix mail
 Webmail
 Mail interface programs often provide other
  functions, such as calendars and to-do lists
  in the same system
Mail system failures
Subject: Re: SIGCSE 2000 sites
  Date: 10 Sep 98 09:57:08 -0400
  From: ndale@cs.utexas.edu (Nell Dale)
   To: <beck>
   CC: Boots Cassel <cassel>
My problem with the Arbaretum is its distance from the airport and
town--and there is no public transportation to speak of. We will have to
arrange buses to take people to and from the airport and to and from town.
Taxis are not expensive, but are not used very much here.
                         This was actually a failure on our receiver mail
                     system. It decided that the recipient of the message
                      did not need to know the e-mail address of anyone
                         except the sender of the message. It stripped off
                            everything from the @ on. ( It is fixed now.)
Problem with aliases
    Subject: Re:VU-UD tickets
     Date: Wed, 22 Sep 1999 11:57:22 -0400
.    From: Dawn_Cassel@company.com
     To: wcassel@anothercompany.com
     CC: Dave@company.com, Kevin@company.com, Mom@company.com,
              Dick@company.com, AME@company.com

                            Here the problem is that the alias used
                          locally is shown to the recipients. Those
                            aliases are of no use in sending replies
                                                     to this message
Result Reporting
 Success reporting is usually optional
 Failure reports are more consistent
   – Unknown user at the destination site
   – Inability to find the destination site
   – Can find, but cannot connect to the destination
   – Badly formed message not processed locally
 Status reporting
   – Verbose mode often available to show all the
     steps in mail delivery
 Workhorse of mail interaction
 Defines message format and transfer
 Uses TCP on port 25
 Send mail to a MTA
 Send mail between MTAs
  The List of Reply Codes

211    System status, or system help reply             452 Requested action not taken: insufficient
                                                          system storage
                                                       500 Syntax error, command unrecognized
214    Help message                                             [This may include errors such as command
    [Information on how to use the receiver or the        line too long]
  meaning of a particular non-standard command;        501 Syntax error in parameters or argument
 this reply is useful only to the human user]           502 Command not implemented
220   <domain> Service ready                            503   Bad sequence of commands
221   <domain> Service closing transmission channel     504   Command parameter not implemented
250   Requested mail action okay, completed             550 Requested action not taken: mailbox
251   User not local; will forward to <forward-path>          [E.g., mailbox not found, no access]
354   Start mail input; end with <CRLF>.<CRLF>          551   User not local; please try <forward-path>
421 <domain> Service not available, closing             552 Requested mail action aborted: exceeded
  transmission channel                                    storage allocation
       [This may be a reply to any command if the
  service knows it must shut down]                      553 Requested action not taken: mailbox name
                                                          not allowed
450 Requested mail action not taken: mailbox                   [E.g., mailbox syntax incorrect]
      [E.g., mailbox busy]                              554   Transaction failed
451 Requested action aborted: local error in
  processing                        Ref: http://raddist.rad.com/networks/1998/smtp/smtp.htm#commands2
11 monet:/mnt/a/cassel> mail -v cassel@acm.org
Subject: test message
Checking mail steps

 monet:/mnt/a/cassel> cassel@acm.org... Connecting to mail.acm.org. via esmtp.
220 mail.acm.org ESMTP Sendmail 8.9.3/8.9.3; Wed, 4 Oct 2000 14:47:43 -0400        From acm.org server
>>> EHLO monet.vill.edu                                    From monet
250-mail.acm.org Hello monet.csc.vill.edu [], pleased to meet you
250-SIZE 2000000
250 HELP
>>> MAIL From:<cassel@monet.vill.edu> SIZE=81
250 <cassel@monet.vill.edu>... Sender ok
>>> RCPT To:<cassel@acm.org>
250 <cassel@acm.org>... Recipient ok
>>> DATA
354 Enter mail, end with "." on a line by itself
>>> .
250 OAA201890 Message accepted for delivery
cassel@acm.org... Sent (OAA201890 Message accepted for delivery)
Closing connection to mail.acm.org.
>>> QUIT
221 mail.acm.org closing connection
cassel@acm.org... Connecting to monet.csc.vill.edu. via smtp...
220 monet.csc.villanova.edu ESMTP Sendmail 8.9.0/8.9.0; Tue, 10 Feb 2004 16:01:54 -0500 (EST)
>>> EHLO csgate.csc.vill.edu
250-monet.csc.villanova.edu Hello csgate.villanova.edu [], pleased to meet you
250 HELP
>>> MAIL From:<cassel@csgate.csc.vill.edu> SIZE=104
250 <cassel@csgate.csc.vill.edu>... Sender ok
>>> RCPT To:<cassel@acm.org>
550 <cassel@acm.org>... Relaying denied
cassel@acm.org... User unknown
>>> RSET
250 Reset state
/mnt/a/cassel/dead.letter... Saved message in /mnt/a/cassel/dead.letter
Closing connection to monet.csc.vill.edu.
>>> QUIT
221 monet.csc.villanova.edu closing connection
cassel@acm.org... Connecting to alias.acm.org. via esmtp...
220-alias.acm.org ESMTP ACM Email Forwarding Service; Tue, 10 Feb 2004 17:11:13 -0500
220-* Secure Mail Server *
220-* *
220-* All connections are logged! *
220-* This server employs antispam technology *
220 *********************************************************************
>>> EHLO monet.csc.villanova.edu
250-alias.acm.org Hello monet.csc.villanova.edu [], pleased to meet you.
250-SEND              >>> MAIL From:<cassel@monet.csc.villanova.edu> SIZE=75
250-SOML              250 2.1.0 <cassel@monet.csc.villanova.edu>... Sender ok
250-SAML              >>> RCPT To:<cassel@acm.org>
250-SIZE              250 2.1.5 <cassel@acm.org>... Recipient ok
250-EXPN              >>> DATA
250-ETRN              354 Enter mail, end with "." on a line by itself
250-ATRN              >>> .
250-DSN               250 2.6.0 372 bytes received in 00:00:02; Message accepted for delivery
250-CHUNKING          cassel@acm.org... Sent (2.6.0 372 bytes received in 00:00:02;
250-CHECKPOINT                                Message accepted for delivery)
250-8BITMIME          Closing connection to alias.acm.org.
250 HELP              >>> QUIT
                     221 2.0.0 alias.acm.org closing connection
Expanded Message Header
       from mail.acm.org ([]) by skinner.villanova.edu (Netscape Messaging
       Server 4.15) with ESMTP id G1X5J300.I88 for <Lillian.Cassel@villanova.edu>;
       Wed, 4 Oct 2000 14:47:27 -0400
       from monet.vill.edu (monet.csc.vill.edu []) by mail.acm.org
       (8.9.3/8.9.3) with ESMTP id OAA201890 for <cassel@acm.org>; Wed, 4 Oct
       2000 14:47:43 -0400
       (from cassel@localhost) by monet.vill.edu (8.9.0/8.9.0) id OAA15022 for
       cassel@acm.org; Wed, 4 Oct 2000 14:47:44 -0400 (EDT)
       Wed, 4 Oct 2000 14:47:44 -0400 (EDT)
       boots cassel <cassel@monet.csc.villanova.edu>
       test message
 Local
  – same machine
  – same local network environment
 remote
   – same mail system on a remote host
   – different type of mail system
Message Store Protocols
 Client interacting with a mail server
                                                (see RFC 1733)
  – offline
     • move mail from server to client machine
  – online
     • keep mail on server and stay connected
  – disconnected
     • keep mail on server
     • download a cache copy and disconnect
     • reconnect to synchronize client and server
 Post Office Protocol
                             see RFC 1725 and later revision
  – works on local copy on the client machine
    (offline access)
  – may leave copy on the server, but does not
 Internet Message Access Protocol
                                              see RFC 1730
  – allows all three interaction modes
POP commands

USER    Client identifies mailbox to be downloaded
PASS    Password
STAT    Get number of messages and size of mailbox
LIST N  Return size of message N
LAST    Get highest message number accessed
RETR N  Retrieve a full message
TOP N M Retrieve only headers and the first N lines
DELE N  Delete message
QUIT     Release service
NOOP    See if POP server is functioning
RPOP    Insecure authentication
Offline, online, disconnected
 Offline is usual for ISPs.
  – They store your messages until you collect them, but don’t provide
    long term disk space to keep all your mail for you.

 Online works when the mail is delivered,
  read, and stored on the same system
  – You login, get your mail, read it, store it, go back to it when you
    want to.

 Disconnected
  – One copy on your local machine; master copy on a server
  – Access available while traveling, from home and office.
  – Long distance phone connections are minimized
Mail Summary
 Early in the ARPAnet days, e-mail came to
  dominate usage
 With Web use, it remains a major
  contributor to traffic on the Internet
 The user interface to the mail system comes
  in many varieties
 Behind the scenes, a few message transfer
  systems deliver the mail

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