1. Sub Topic : E-Mail transfer (Part 1)
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2. Recap
• In the previous class, you have learnt about
– DNS server and its functions
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3. 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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4. Introduction to E-mail (Electronic mail)
Fig.1
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5. 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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6. 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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7. 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” 7

8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14. E-Mail Overview
• Any person with an e-mail account can send and receive
e-mail messages
Fig.4 14

15. E-Mail Overview
• Basic e-mail activities
– Writing
– Reading
– Replying
– Forwarding
Fig.5 15

16. 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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17. 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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18. How does Email Work?
Fig.6 18

19. Transfer of Email
(detailed procedure)
• 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
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20. Important Terms
• 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
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21. Important Terms
• 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
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22. Illustration of Email Transfer
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23. 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 23

24. 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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25. 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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26. 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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27. 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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28. 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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29. 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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30. Quiz
4) ____allows non-text data to be sent along with an e-
mail message
A) MIME
5) What type of files have .wav extension?
A) Audio Files (Microsoft)
6) Expand .mpeg used as extension for image files
A) Moving Picture Expert Group
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31. 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 ?
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