Electronic mails (Emails) CSC1720 – Introduction to Internet Essential Materials.

Electronic mails Electronic mails (Emails)(Emails)

CSC1720 – Introduction to CSC1720 – Introduction to InternetInternet

Essential MaterialsEssential Materials


All copyrights reserved by C.C. Cheung All copyrights reserved by C.C. Cheung 2003.2003.

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OutlineOutline

Part I – General partPart I – General part– Email basicsEmail basics– How does email work?How does email work?– Basic email operationsBasic email operations– Signatures, Attachment (MIME)Signatures, Attachment (MIME)

Part II – Technical partPart II – Technical part– SMTP, HTTP, POP and IMAPSMTP, HTTP, POP and IMAP

Part III – more advancedPart III – more advanced– SPAM & CAUCESPAM & CAUCE– Email etiquette (Netiquette)Email etiquette (Netiquette)– CUHK CWEM & Phonebook directoryCUHK CWEM & Phonebook directory



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What is Email?What is Email?

A mail, but is sent electronically A mail, but is sent electronically across the Internet. across the Internet.

Quickly delivered in seconds or Quickly delivered in seconds or minutes (if without problem). minutes (if without problem).

TelephoneTelephone E-mailE-mail PostPost

SpeedSpeed HighHigh ModerateModerate LowLow

SynchronizeSynchronizedd

YesYes NoNo NoNo

FormalityFormality VariesVaries ModerateModerate VariesVaries

ConferencinConferencingg

Small GroupSmall Group Any to allAny to all One-way One-way onlyonly

SecuritySecurity ModerateModerate LowLow HighHigh



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Pros & ConsPros & Cons

AdvantagesAdvantages– Convenience, Fast speed, Inexpensive, Convenience, Fast speed, Inexpensive,

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

DisadvantagesDisadvantages– Misdirection, Interception, Forgery, overload, Misdirection, Interception, Forgery, overload,

Funk (Spamming), No response (from the Funk (Spamming), No response (from the receiver).receiver).

Think one good and one bad experience Think one good and one bad experience that you have had with email.that you have had with email.



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The growth of Email The growth of Email Users & MessagesUsers & Messages

Figure from Figure from "Discovering "Discovering 2000", Shelly 2000", Shelly Cashman Series, Cashman Series, Thomson Learning Thomson Learning



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Email addressEmail address

What you need is What you need is

– The E-mail addressThe E-mail address of the recipient. of the recipient. – user@host user@host – [email protected] [email protected] – [email protected] [email protected]

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

““cccheung" is the cccheung" is the user nameuser name of the recipient. of the recipient. User name and hostname are separated by User name and hostname are separated by "@""@". .



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Email server and clientEmail server and client

Email clientEmail client – software / program – software / program that can transfer e-mail from a that can transfer e-mail from a local host to a local e-mail server.local host to a local e-mail server.

Email serverEmail server – software/program – software/program that can send/receive e-mail that can send/receive e-mail from/to other email servers.from/to other email servers.

MailboxMailbox – An electronic mailbox is a – An electronic mailbox is a disk file which holds email disk file which holds email messages.messages.



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Electronic mailboxElectronic mailbox



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Email Software (Client)Email Software (Client)

Graphical Client (User friendly)Graphical Client (User friendly) OutlookOutlook NetscapeNetscape



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Email Software (Client)Email Software (Client)

Text mode (UNIX - mailserv, logic server)Text mode (UNIX - mailserv, logic server) muttmutt pinepine



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Email Software Email Software (Server)(Server) Install the mail server on Linux/Unix or Windows Install the mail server on Linux/Unix or Windows

platform.platform.



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SignatureSignature

Header

Greeting

Text

Signature



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Cc & BccCc & Bcc

Carbon Copy SectionCarbon Copy Section– Send a message to more than one Send a message to more than one

person, all the recipients will see the person, all the recipients will see the list of email addresses.list of email addresses.

Blind Carbon Copy SectionBlind Carbon Copy Section– The addresses won’t be seen by the The addresses won’t be seen by the

recipients.recipients.– When email is sent to a large group When email is sent to a large group

of people who don’t know each of people who don’t know each other.other.



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Attachment – MIMEAttachment – MIMEMMulti-purpose ulti-purpose IInternet nternet MMail ail EExtensionxtension

A protocol for transmitting non-text information A protocol for transmitting non-text information across the Internet. Basically, non-across the Internet. Basically, non-ASCIIASCII data is data is converted to converted to ASCIIASCII for transmission and then for transmission and then converted back at the receiver.converted back at the receiver.

A specification for automatically sending A specification for automatically sending objects other than text in email messages. objects other than text in email messages.

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

Additional hardware and Additional hardware and helper softwarehelper software are are usually required. usually required.

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



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Examples of the ASCII encoding

Consists of fixed length codes of 7-bits (0 or 1)

ASCII CodeASCII Code



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EncodingEncodingASCII & Double-byte ASCII & Double-byte

EncodingEncoding RepresentatioRepresentationn

LatinLatin aa

ASCII HexASCII Hex 0x610x61

DecimalDecimal 9797

BinaryBinary 0110 00000110 0000

OctalOctal 140140

EncodingEncoding RepresentatioRepresentationn

KanjiKanji 今今UnicodeUnicode \u4ECA\u4ECA

Shift_JISShift_JIS 8DA18DA1

EUC_JPEUC_JP BAA3BAA3

Big 5Big 5 A4B5A4B5

UTF-8UTF-8 E4BB8AE4BB8A



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MIMEMIME



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Common MIME TypesCommon MIME Types

TypeType SubtypeSubtype DescriptionDescription File extensionsFile extensions

ApplicatioApplicationn

postscriptpostscript

texttextPrintable postscript documentPrintable postscript document

TEX documentTEX document.eps, .ps.eps, .ps

.tex.tex

AudioAudio midimidi

realaudiorealaudio

wavwav

Musical Instrument Digital InterfaceMusical Instrument Digital Interface

Progressive Networks soundProgressive Networks sound

Microsoft soundMicrosoft sound

.midi, .mid.midi, .mid

.ra, .ram.ra, .ram

.wav.wav

ImageImage gifgif

jpegjpeg

pngpng

Grapical Interchange FormatGrapical Interchange Format

Joint Photographic Experts GroupJoint Photographic Experts Group

Portable Network GraphicsPortable Network Graphics

.gif.gif

.jpeg, .jpg, .jpe.jpeg, .jpg, .jpe

.png.png

ModelModel vrmlvrml Virtual Reality Modeling LanguageVirtual Reality Modeling Language .wrl.wrl

TextText htmlhtml

plainplainHypertext Markup LanguageHypertext Markup Language

Unformatted textUnformatted text.html, .htm.html, .htm

.txt.txt

VideoVideo aviavi

mpegmpeg

quicktimequicktime

Microsoft audio video interleavedMicrosoft audio video interleaved

Moving Picture Experts GroupMoving Picture Experts Group

Apple QuickTime movieApple QuickTime movie

.avi.avi

.mpeg, .mpg.mpeg, .mpg

.qt, .mov.qt, .mov



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MIME headersMIME headers

MIME-Version: 1.0MIME-Version: 1.0 Content-type: multipart/mixed: Content-type: multipart/mixed:

boundary=“simple boundary”boundary=“simple boundary” --simple boundary--simple boundary ………… --simple boundary--simple boundary ………… --simple boundary----simple boundary--



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MIME ExampleMIME Example



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How How does does email email worksworks??



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SMTPSMTP

E-mails are transferred across the Internet via E-mails are transferred across the Internet via Simple Mail Transfer Protocol (SMTP)Simple Mail Transfer Protocol (SMTP). .

The mail server uses SMTP to determine how to The mail server uses SMTP to determine how to route the message through the Internet and route the message through the Internet and then sends the message. then sends the message.

When the message arrives at the recipient's When the message arrives at the recipient's mail server, the message is transferred to a mail server, the message is transferred to a POP3 serverPOP3 server. POP stands for . POP stands for Post Office Post Office ProtocolProtocol. .

The POP server holds the message until the The POP server holds the message until the recipient retrieves it with his/her email software. recipient retrieves it with his/her email software.



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SMTP illustrationSMTP illustration

John’s computerMary’s computer

Mail server

Internet

Mail server

SMTP

SMTP SMTP



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POPPOP

AdvantagesAdvantages– Don’t have to know the name of your machineDon’t have to know the name of your machine– POP mail server is installed on a computer POP mail server is installed on a computer

always ONalways ON– Use Windows interface to read emailUse Windows interface to read email

DisadvantagesDisadvantages– The email at the mail server is popped to your The email at the mail server is popped to your

local machinelocal machine Refer to notes page for more explanationsRefer to notes page for more explanations



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POP illustrationPOP illustration

John’s computerMary’s computer

Mail server

Internet

Mail server

Mailspool

Localinbox

SMTP

SMTPSMTP

POP



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How to setup email How to setup email client in Netscape?client in Netscape?

Select POP server

Select SMTP server



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IMAPIMAP

Another popular method by which users obtain their emails is called Another popular method by which users obtain their emails is called a a central mail spoolcentral mail spool. .

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

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

Peter's emails remain on his mail server. The emails are not brought Peter's emails remain on his mail server. The emails are not brought over to the computer from which he is working. That is, leaving the over to the computer from which he is working. That is, leaving the emails in a central location, and allowing access of the emails from emails in a central location, and allowing access of the emails from several places. several places.

That is, when Peter wants to read his emails, he must send a That is, when Peter wants to read his emails, he must send a password to the mail server to password to the mail server to authenticateauthenticate himself. himself.

Another advantage of IMAP is that it Another advantage of IMAP is that it encrypts encrypts passwords so that passwords so that someone someone sniffingsniffing the network cannot directly obtain his password. the network cannot directly obtain his password.



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IMAP illustrationIMAP illustration

John’s home computerJohn’s office computer

Mail server (SMTP/IMAP)

Johninbox

IMAP linkIMAP link

Incoming/Outgoing emails



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How to setup IMAP in How to setup IMAP in Outlook Express?Outlook Express?

POP email

HTTP email

IMAP email

Select the correct Protocol



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Web-based e-mail - Web-based e-mail - HTTPHTTP Can deliver mail message in web page format.Can deliver mail message in web page format. More reliable to use POP and IMAP than HTTP mail More reliable to use POP and IMAP than HTTP mail

account.account.



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Bounced back emailBounced back email Bad user account nameBad user account name Bad domain nameBad domain name Domain name server is down for several daysDomain name server is down for several days Some other malfunction (email too big)Some other malfunction (email too big)



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Email Virus - MelissaEmail Virus - Melissa

May 24, 1999, Melissa virus is spreading May 24, 1999, Melissa virus is spreading as RTF files.as RTF files.

300 organizations affected, 100,000 300 organizations affected, 100,000 hosts.hosts.

One site reported, 32,000 copies of email One site reported, 32,000 copies of email are received in 45 minutes.are received in 45 minutes.

Not a worm, require user interaction to Not a worm, require user interaction to propagate the virus.propagate the virus.

Why called Melissa?Why called Melissa?– Named by the antivirus software vendors.Named by the antivirus software vendors.

Don’t open attachment Don’t open attachment not infected. not infected.



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Junk MailsJunk Mails

How can they get into your mailbox?How can they get into your mailbox?– From name card, letter heads, published From name card, letter heads, published

papers.papers.– Use search engine in the newsgroup, Use search engine in the newsgroup,

bulletin boards, phone books.bulletin boards, phone books.– Dump a full user list in a server.Dump a full user list in a server.

How to stop the intrusion of Junk Mails?How to stop the intrusion of Junk Mails?– Mail server providers joint effortMail server providers joint effort– FilteringFiltering– Preview before downloadingPreview before downloading



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SPAMSPAM

SPAMSPAM is flooding the Internet with many is flooding the Internet with many copies of the same messagecopies of the same message– Force to send message to peopleForce to send message to people– Junk electronic mail.Junk electronic mail.

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

emailsemails– Fraud – not an advertisement subjectFraud – not an advertisement subject– Waste of others’ resources – stealing bandwidthWaste of others’ resources – stealing bandwidth– Displacement of Normal Email – destroy the Displacement of Normal Email – destroy the

usefulness and effectiveness of emailusefulness and effectiveness of email– Ethics problemEthics problem



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Anti - SPAMAnti - SPAM



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CAUCECAUCE - Coalition Against - Coalition Against Unsolicited Commercial E-Unsolicited Commercial E-mailmail An all An all

volunteer volunteer organization organization which is which is created by created by Netizens over Netizens over the world.the world.



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CUHK CWEMCUHK CWEMCampus Wide Email Campus Wide Email SystemSystem Provided by the Computer Services Center (CSC). Provided by the Computer Services Center (CSC). The system resides in The system resides in mailserv.cuhk.edu.hkmailserv.cuhk.edu.hk

– which is a Sun Ultra-Enterprise 2 Model 2200 Server. which is a Sun Ultra-Enterprise 2 Model 2200 Server. Every student is given an email account and mailbox with Every student is given an email account and mailbox with

2 megabytes storage space. 2 megabytes storage space. Computing id / login name / username: Computing id / login name / username: Your computing id is an "s" plus first 6 digits of the Your computing id is an "s" plus first 6 digits of the

student id number. student id number. Computing id for s00201960 is s002019 Computing id for s00201960 is s002019 E-mail address: E-mail address:

– [email protected]@mailserv.cuhk.edu.hk,,– [email protected] [email protected] – [email protected] [email protected] [email protected] [email protected]



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CUHK – Phonebook CUHK – Phonebook directorydirectory Works together with Works together with

CWEM CWEM Provide you: Provide you:

– an easy-to-remember an easy-to-remember email address (email address (aliasalias) )

– a means to enquire email a means to enquire email address of all staffs and address of all staffs and students (students (queryquery) )

– a means to redirect a means to redirect emails (emails (forwardforward) )

Try the phonebookTry the phonebook



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ReferencesReferences

Discussion – handoutsDiscussion – handouts– SPAM & Chinese DNSSPAM & Chinese DNS

Internet FAQ ArchivesInternet FAQ Archives How USENET protocol works?How USENET protocol works? http://email.about.com/http://email.about.com/

The End.The End. Thank you for your patience!Thank you for your patience!

Electronic mails (Emails) CSC1720 – Introduction to Internet Essential Materials.

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Transcript of Electronic mails (Emails) CSC1720 – Introduction to Internet Essential Materials.