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Electronic mails (Emails)

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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. user@host

cccheung@cse.cuhk.edu.hk

eng70132@leonis.nus.sg

"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