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Sub Topic : E-Mail transfer (Part 1)

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Recap

• In the previous class, you have learnt about

– DNS server and its functions

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Objectives• On the completion of this period, you would be

able to Understand about

– What is e-mail ?

– The advantages of e-mail

– E-mail Components

– E-mail Functions

– E-mail transfer mechanism

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Introduction to E-mail (Electronic mail)

Fig.1

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What is Email?

• E-mail is one of the most popular services available through the Internet. It is similar to a mail, but is sent electronically across the Internet.

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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Letter Analogy

• Write a 20-page letter to Grandma

• Number the pages

• Put each page in a separate envelope

• Drop them in the mail

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Letter Analogy Continued

• Do letters take the same route

• Do letters arrive at the same time

• Do letters arrive in any particular order

• How does Grandma handle multiple letters arriving

• What if a letter gets lost

• Intermediate Post Offices act like routers

• Mail boxes are similar to “ports”

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Electronic Mail

• Electronic mail shortly known as e-mail was created to

allow two individuals to communicate using computers

• It is an electronic way of communicating information from

one computer to the other which are connected through

network

• E-mail has emerged as inexpensive and efficient means

of communication

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E-MAIL Features

• The present e-mail system offers the following features

– Composing and sending a message

– Sending a single message to many persons

– Attaching Graphics, Voice, Video to message

– Storing, Forwarding, Deleting, Replying to a received

message

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E-mail Technology

• E-mail systems carry and manipulate e-mail messages:

– E-mail servers.– Based on store-and-forward technology.

• Three types of e-mail systems widely used today:

– POP (Post Office Protocol).– IMAP (Internet Message Access Protocol).– Web-based e-mail.

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E-mail Technology

• Web-based e-mail accounts allow you to use a browser to access your e-mail messages

Fig.2

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E-mail Technology

• A POP server is a

computer that stores your

incoming messages until

they can be transferred to

your hard disk– E-mail client software– SMTP server

Fig.3

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E-mail Functions• From the user point of view, e-mail perform the following

functions

– Composition (providing text editor features)

– Transfer (message from sender to receiver)

– Reporting (delivery reports)

– Displaying (incoming and sent mails)

– Disposition (forwarding, archiving, deleting)

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E-Mail Overview

• Any person with an e-mail account can send and receive e-mail messages

Fig.4

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E-Mail Overview

• Basic e-mail activities

– Writing– Reading– Replying– Forwarding

Fig.5

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How is e-mail Transferred ?

Here's what happens to an email when it is transferred over the Internet

1. It is broken up into a whole lot of same-sized pieces (packets)

2. A header is added to each packet that explains where it came from, where it is going and how it fits with the rest of the packets

3. Each packet is sent from computer to computer until it finds its way to its destination

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E-mail Transfer (Contd.,)

4 Each computer along the way decides where next to send the packet. This could depend on things like how busy the other computers are when the packet was received. The packets may or may not all take the same route

5. At the destination, the packets are examined.

If there are any packets missing or damaged, a message is sent asking for those packets to be resent. This continues until all the packets have been received intact

6. The packets are reassembled into their original form

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How does Email Work?

Fig.6

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• Analogy to postal delivary system

– Letter : Mail User Agent

– Postal Address : Email address

– Postman : Mail Delivery Agent

– Post Box : Mailbox / Maildir

– Post Office : Mail Transfer Agent

Transfer of Email (detailed procedure)

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• Mail User Agent (MUA)– Interface used for users to send and receive mail– Translates pop/imap commands for user– E.g. rediffmail, yahoomail, gmail (web based)

outlook, eudora– Allows users to retrieve and compose emails

• Mail Delivery Agent (MDA)

– Delivers email from MTA and distributes to individual mailboxes

– E.g. POP server

Important Terms

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• Mail Transfer Agent (MTA)

– Transfers email between machines using SMTP

– Sends mail to destination

– Performs SMTP functions

– E.g. SMTP Server

• Mailbox

– Stores users mail

Important Terms

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Illustration of Email Transfer

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Email Transfer - Step 1

• Sender creates and sends an email

– The originating sender creates an email in their Mail User Agent (MUA) and clicks 'Send'

– The MUA is the application the originating sender uses to compose and read email, such as yahoomail, gmail, Eudora, Outlook, etc

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Email Transfer - Step 2

• Sender's MDA/MTA routes the email

• The sender's MUA transfers the email to a local Mail Transfer Agent (MTA) (SMTP server)

• The MTA accepts the email, then routes it to local mailboxes or forwards it if it isn't locally addressed

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Email Transfer - Step 3

• MTA to MTA Transfer (Sender’s SMTP Server to Receiver’s SMTP Server)

– To find the recipient's IP address, the MTA contacts the Domain Name System (DNS)

– When transferring an email, the sending MTA handles all aspects of mail delivery until the message has been either accepted or rejected by the receiving MTA

– The email enters the Internet network cloud, where it is routed to the receiver’s MTA along a chain of routers

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Email Transfer - Step 4• Firewalls, Spam and Virus Filters

– Before reaching the receiver’s MTA an email may be transferred to at least one firewall

– An email encountering a firewall may be tested by spam and virus filters before it is allowed to pass inside the firewall

– These filters test to see if the message qualifies as spam or malware. If the message contains malware, the file is usually quarantined and the sender is notified

– If the message is identified as spam, it will probably be deleted without notifying the sender

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Email Transfer -Step 5

• Delivery

– The email makes it past the hazards of the spam, and is accepted for delivery by the receiver's MTA

– The MTA calls a local MDA (POP Server) to deliver the mail to the correct mailbox, where it will sit until it is retrieved by the recipient's MUA

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Summary

In this class, you have learnt about

• E-mail is an electronic way of sending mails

• E-mail contains header , greeting , text and signature

• E- mail address contains username , @ and domain name

• Non text information can also be transmitted through e-mail using MIME attachments

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Quiz

1) ____is a storage area to store e-mails

A) Mail Box

2) In e-mail id, the prefix refers to the ___

A) User Name

3) Which symbol is used to connect the user name to

the domain name portion ?

A) @

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4) ____allows non-text data to be sent along with an e- mail messageA) MIME

5) What type of files have .wav extension?A) Audio Files (Microsoft)

6) Expand .mpeg used as extension for image filesA) Moving Picture Expert Group

Quiz

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Frequently Asked Questions

1. Explain how e-mail is transferred

2. Explain the components of E-mail

3. What are the advantages and disadvantages of E-mail ?