email prezentacija

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    Electronic mails (Emails)

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    E-MailCSC1720 Introduction toInternet

    All copyrights reserved by C.C. Cheung 2003.

    What is Email?

    A mail, but is sent electronically

    across the Internet.

    Quickly delivered in seconds orminutes (if without problem).

    Telephone E-mail Post

    Speed High Moderate Low

    Synchronized Yes No No

    Formality Varies Moderate Varies

    Conferencing Small Group Any to all One-way only

    Security Moderate Low High

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    Pros & Cons

    Advantages

    Convenience, Fast speed, Inexpensive, Printable,

    Reliable, Global, Generality (not limited to text,but graphics, programs, even sounds)

    Disadvantages

    Misdirection, Interception, Forgery, overload,

    Funk (Spamming), No response (from thereceiver).

    Think one good and one bad experiencethat you have had with email.

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    Email address

    What you need is

    The E-mail address of the recipient. [email protected]

    [email protected]

    [email protected]

    "cse.cuhk.edu.hk" is the domain name of themail serverwhich handles the recipient's mail.

    cccheung" is the user name of the recipient.

    User name and hostname are separated by "@".

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    Email server and client

    Email client software / program thatcan transfer e-mail from a local host to

    a local e-mail server. Email server software/program that

    can send/receive e-mail from/to other

    email servers. Mailbox An electronic mailbox is a

    disk file which holds email messages.

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    Email Software (Client)

    Graphical Client (User friendly)

    Outlook

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    Email Software (Client)

    Text mode (UNIX - mailserv, logic server)

    mutt pine

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    Email Software (Server)

    Install the mail server on Linux/Unix or Windows platform.

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    Cc & Bcc

    Carbon Copy Section Send a message to more than one

    person, all the recipients will see the listof email addresses.

    Blind Carbon Copy Section The addresses wont be seen by the

    recipients. When email is sent to a large group of

    people who dont know each other.

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    Attachment MIME

    Multi-purpose Internet Mail Extension

    A protocol for transmitting non-text informationacross the Internet. Basically, non-ASCII data isconverted to ASCII for transmission and then

    converted back at the receiver. A specification for automatically sending

    objects other than text in email messages.

    MIME is usually associated with multimedia,such as images, audio recordings, and movies.

    Additional hardware and helper software areusually required.

    Common MIME-compliant mailers: pine, metamail, Netscape messenger, MS Outlook

    http://www.cknow.com/ckinfo/acro_a/ascii_1.shtmlhttp://www.faqs.org/rfcs/rfc977.htmlhttp://www.faqs.org/rfcs/rfc977.htmlhttp://www.cknow.com/ckinfo/acro_a/ascii_1.shtml
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    Common MIME Types

    Type Subtype Description File extensions

    Application postscript

    text

    Printable postscript document

    TEX document

    .eps, .ps

    .tex

    Audio midi

    realaudiowav

    Musical Instrument Digital Interface

    Progressive Networks soundMicrosoft sound

    .midi, .mid

    .ra, .ram

    .wav

    Image gif

    jpeg

    png

    Grapical Interchange Format

    Joint Photographic Experts Group

    Portable Network Graphics

    .gif

    .jpeg, .jpg, .jpe

    .png

    Model vrml Virtual Reality Modeling Language .wrl

    Text html

    plain

    Hypertext Markup Language

    Unformatted text

    .html, .htm

    .txt

    Video avi

    mpeg

    quicktime

    Microsoft audio video interleaved

    Moving Picture Experts Group

    Apple QuickTime movie

    .avi

    .mpeg, .mpg

    .qt, .mov

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    How

    doesemailworks?

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    SMTP

    E-mails are transferred across the Internet via

    Simple Mail Transfer Protocol (SMTP).

    The mail server uses SMTP to determine how to

    route the message through the Internet and

    then sends the message.

    When the message arrives at the recipient's

    mail server, the message is transferred to a

    POP3 server. POP stands forPost OfficeProtocol.

    The POP server holds the message until the

    recipient retrieves it with his/her email software.

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    SMTP illustration

    Johns computerMarys computer

    Mail server

    Internet

    Mail server

    SMTP

    SMTPSMTP

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    POP

    Advantages

    Dont have to know the name of your machine

    POP mail server is installed on a computeralways ON

    Use Windows interface to read email

    Disadvantages

    The email at the mail server is popped to yourlocal machine

    Refer to notes page for more explanations

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    POP illustration

    Johns computerMarys computer

    Mail server

    Internet

    Mail server

    Mailspool

    Localinbox

    SMTP

    SMTPSMTP

    POP

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    IMAP

    Another popular method by which users obtain their emails iscalled a central mail spool.

    Imagine what could happen if Peter where reading emails at hisoffice while his wife was simultaneously trying to read from thesame inbox from home.

    Lots of complication can arise in this scenario, and a protocol hasbeen designed to handle many of the relevant issues. It's called theInteractive Mail Access Protocol (IMAP).

    Peter's emails remain on his mail server. The emails are notbrought over to the computer from which he is working. That is,leaving the emails in a central location, and allowing access of theemails from several places.

    That is, when Peter wants to read his emails, he must send apassword to the mail server to authenticate himself.

    Another advantage of IMAP is that it encrypts passwords so thatsomeone sni f f ing the network cannot directly obtain his password.

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    IMAP illustration

    Johns home computerJohns office computer

    Mail server (SMTP/IMAP)

    Johninbox

    IMAP linkIMAP link

    Incoming/Outgoing emails

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    How to setup IMAP in

    Outlook Express?

    POP email

    HTTP emailIMAP email

    Select the correct Protocol

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    Web-based e-mail - HTTP

    Can deliver mail message in web page format.

    More reliable to use POP and IMAP than HTTP mail account.

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    Bounced back email

    Bad user account name

    Bad domain name

    Domain name server is down for several days

    Some other malfunction (email too big)

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    Junk Mails

    How can they get into your mailbox?

    From name card, letter heads, published papers.

    Use search engine in the newsgroup, bulletinboards, phone books.

    Dump a full user list in a server.

    How to stop the intrusion of Junk Mails?

    Mail server providers joint effort

    Filtering

    Preview before downloading

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    SPAM

    SPAM is flooding the Internet with many copies ofthe same message

    Force to send message to people

    Junk electronic mail.

    Why cause problem? Cost-shifting very cheap to send thousands of emails

    Fraud not an advertisement subject

    Waste of others resources stealing bandwidth

    Displacement of Normal Email destroy the usefulnessand effectiveness of email

    Ethics problem

    http://spam.abuse.net/http://spam.abuse.net/
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    Anti - SPAM

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    References

    Discussion handouts SPAM & Chinese DNS

    Internet FAQ Archives How USENET protocol works?

    http://email.about.com/

    The End.

    Thank you for your patience!

    http://www.dsv.su.se/~jpalme/e-mail-book/usenet-news.htmlhttp://email.about.com/http://email.about.com/http://www.dsv.su.se/~jpalme/e-mail-book/usenet-news.html