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Electronic Mail Networking Concepts

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GUI applications Outlook, Netscape. Web based Pine, Outlook Express, gmail, AOL, Hotmail, etc. ... The Outlook Express Client. Outlook Email Window. Email ... – PowerPoint PPT presentation

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Title: Electronic Mail Networking Concepts


1
Electronic MailNetworking Concepts
  • D.A. Clements

2
Just a thought
3
Electronic Mail
  • Most successful and ubiquitous Internet
    application
  • Used to transmit messages
  • From one person to another or
  • From one person to many people
  • Initially exchanged only plain text messages
  • Today messages routinely include
  • Pictures
  • Advanced text markup (like different fonts and
    colors)
  • File attachments (like Word or Excel files)
  • Most follow open Internet standards
  • Some proprietary systems incorporate additional
    features like calendaring, address books,
    security features and virus protection

4
Client/Server Architecture
  • Central technology of both LANs and the Internet
    today
  • Describes the relationship between two network
    computer programs
  • Client a local program/computer makes a service
    request
  • Server remote program/computer fulfills the
    request
  • Both sides can perform relevant data processing
  • eMail Server performs the Post Office functions
  • eMail Client performs creation, formatting,
    display funtions
  • Many different email clients and servers

5
Email Delivery Scenario
Stored here until UserConnects
6
The Email Client
  • Software the user uses to send and receive email
  • Available for all computer operating systems
  • Unix / Linux
  • Windows
  • Mac
  • Can take the following forms
  • Dumb-terminal/character applications pine, elm
  • GUI applications Outlook, Netscape
  • Web based Pine, Outlook Express, gmail, AOL,
    Hotmail, etc.
  • No matter what they look like, they all have to
    do the same thing to send mail on the Internet
  • They all must talk SMTP

7
Email Client Features
  • Common features
  • Alias and alias-lists, (address books)
  • Folders (longer-term storage)
  • Forwarding, carbon copies (cc/bcc), reply
  • File inclusion, attachments
  • Signature file...signature-file
  • Evolving
  • Security
  • PGP, S/MIME
  • Authentication
  • Digital certificates user authentication

8
The Outlook Express Client
9
Outlook Email Window
10
Email Servers
  • Sendmail for UNIX systems
  • Microsoft Exchange Server
  • Eudora Internet Mail Server (EIMS) for Macintosh
  • MDaemon
  • Merak Mail Server
  • MailEnable
  • SurgeMail
  • Many more

11
Email Addresses
  • Internet standard
  • userid_at_host.domain
  • Such as daclem_at_u.washington.edu
  • Some variations are possible like
  • Mark.Palmer_at_xyz.com
  • 12345.65362_at_xyz.com
  • Where xyz.com is the domain name of eMail server
  • DNS resolves name exactly like for web sites
  • Early commercial competing alternatives
  • MCIMail
  • SprintMail
  • CompuServe
  • Each had proprietary address formats
  • Couldnt readily exchange information between
    systems

12
Delivering the Message
  • Once sent an email message is usually placed in
    an outgoing mail queue folder on the local
    computer
  • A server process on that box checks the folder
    periodically
  • If it finds an outgoing message
  • It initiates an SMTP (Simple Mail Transfer
    Protocol) connection to the destination mail
    server
  • If the destination server is up and accepting
    messages
  • The message will be delivered immediately
  • If the destination is not accepting messages
  • Message will be placed back in the outgoing mail
    folder
  • Queued-up for another attempt (usually 10-15
    minutes)
  • If the message cant be delivered after specific
    period of time (typically 3 days)
  • It is returned to the sender as undeliverable

13
SMTP
  • Simple Mail Transport Protocol
  • Originally defined by RFC 821 in 1982
  • Modified by RFC 2821 in 2001
  • A host to host mail transport and delivery
    protocol
  • Connect and listen on port 25 (OSI Layer 4)
  • SMTP servers can be
  • The source
  • The final destination
  • Or they can relay mail for others
  • Many servers limit this service to computers
    connected to the network
  • Prevents spammers from using the server to
    distribute their mail
  • UW mail system does this
  • Has nothing to do with how you read the mail once
    it arrives
  • POP and IMAP protocols for PC/Mac-based clients
    retrieve mail

14
So far we are here
Stored here until UserConnects
15
Checking/Reading Mail
  • Sue previously configured her email client to
    talk to a POP or IMAP server
  • She connects to Internet and runs her email
    client
  • The email client talks to her server using the
    POP or IMAP protocol and either
  • Downloads the messages to Sues computer (POP),
    or
  • Downloads the list of messages stored on the
    server to Sues client (IMAP)
  • Sue selects a message and is able to read it
    either from
  • Her local computers hard drive (POP), or
  • The mail server (IMAP)

Stored here until UserConnects
POP3 or IMAP
16
POP
  • Post Office Protocol
  • Version 3 mostly widely used today POP3
  • Defined by RFC 1939 (which obsoletes RFC1725)
  • Runs over port 110 (OSI Layer 4)
  • Simple protocol
  • Essentially a store, copy, delete protocol
  • Mail is stored on the server until the client
    connects
  • It is downloaded to the client by copying
  • It is then usually deleted from the server
  • A simple text-based protocol
  • Widely used and supported
  • Many ISPs suggest you use a POP client for mail
  • Good for them because the mail is removed from
    their server
  • Many email clients support it including
  • Outlook and Outlook Express
  • Eudora the King of POP
  • Netscape Mail

17
POP Weaknesses Strength
  • Not convenient for users that use multiple
    machines during the day. Why?
  • Where is the email you read yesterday?
  • Cant selectively retrieve messages or parts of
    messages
  • What if there is a big attachment and you have a
    SLOW connection? Say sitting in a airport
  • Since mail is downloaded to your machine
  • If you use only one computer
  • You can read and compose messages offline

18
IMAP
  • Internet Message Access Protocol
  • Defined by RFC 2060 and several other additions
  • Most work done at UW by Mark Crispin and others
    in CAC
  • Most IMAP servers run on port 143
  • Folders and Messages can be stored on the server
    or in local folders on your machine
  • Can selectively copy messages from server to the
    local client
  • Much better than POP for people using multiple
    machines
  • IMAP4 has a mechanism to work off-line
  • Then resynchronize the changes when you reconnect
  • MUCH more complex protocol to implement
  • Result not as many clients as POP

19
So why not
Why do we need SMTP servers to deliver mail and
other protocols for retrieving and displaying
messages? Why not just connect directly? What
address would we use? Most hosts use dynamic IP
addresses (DHCP) What if the recipients address
changes before email arrives? Most PCs do not
have IP names that are registered in DNS What if
the destination host is powered off? What if we
turn off our machine, how will we receive new
mail? How do we effectively queue messages for
later delivery since either host machine can be
powered off? What if the sending / receiving
hosts are 10-12 time zones apart?
20
Non-Standard Email Systems
  • SMTP, POP, and IMAP are great open standards
  • But they address just a portion of what people
    want to do with email
  • Address book is not part of the protocols
  • What if you want (need) to recall a sent
    message?
  • What if you want to do workflow through your
    email system?
  • What if you want to use shared calendaring and
    scheduling in email?
  • These protocols have no mechanisms for that type
    of functionality.

21
Proprietary Servers/Clients
  • Many products today add these missing features
  • Most notable are
  • Microsoft Exchange (they claim 100 million
    licenses sold to businesses)
  • Lotus Notes
  • Novell Groupwise
  • Most offer scheduling/calendaring and some do
    workflow
  • Unfortunately, no standard has emerged for
    calendaring
  • You are often limited to exchanging data with
    other clients using the same product
  • A new standard called iCalendar may be emerging
  • While considered proprietary they
  • All use SMTP for sending/receiving mail
  • Most can act as a POP or IMAP server
  • If you use a standard client , you lose the
    added functionality
  • Example Using Unix Pine configured as an IMAP
    client to the iSchool Exchange server
  • You can see all your folders and messages, but
    cant do any scheduling

22
Proprietary Email System
  • Microsoft Exchange Server
  • IMAP
  • Added value
  • Work offline modeif no Internet connection
    available
  • Disconnected modeif server or Internet
    connection goes down
  • Synchs files between client and server
  • Downloads mail to client
  • Uploads mail when connection is restored

23
Proprietary Email System
24
Web Client Outlook Web Access (OWA)
25
End papers
Your mailbox is your window to your heart! Make
sure you leave that window open! Takayuki
Ikkaku, Arisa Hosaka, and Toshihiro Kawabata,
Animal Crossing Wild World, 2005
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