Transcript Document

The Internet Book
Chapter 20
Description Of
Functionality
• Electronic mail systems permit
complex communications and
interactions.
– Send a single message to many recipients
– Send a message that includes text, audio,
video, or graphics
– Send a message to a user on a network
outside the Internet
– Send a message to which a computer
program responds
3
The Best Of All Worlds
• Networks provide the speed of
telephone communication and
permanence of postal mail.
–Can transfer small notes or large
documents
–Have become extremely popular
4
Each User Has A Mailbox For
E-mail
• Like a post office
mailbox, each e-mail
mailbox has an
address.
• Any user can send email if they know the
mailbox address.
5
Sending An E-mail Message
• To send e-mail across the Internet,
the user:
– Runs an e-mail application
– Composes and edits a message
• Adds attachments
– Specifies a recipient
– Finishes entering the message
– Sends the message
Hey, where’s the
send button?
6
Notification That E-mail Has
Arrived
• A user can configure the e-mail
software to:
– Print text messages when mail arrives
• “You got mail”
– Play a recording or tone
when mail arrives
– Suppress notification
altogether
7
Reading An E-Mail Message
• When the e-mail application begins, it:
– Tells the user about waiting messages
– Gives an initial summary of the mail
– Displays the message contents
– Allows the user to:
• Send a reply
• Leave the message in the inbox
• Save the message
• Delete the message
8
E-mail Messages Look Like
Interoffice Memos
• An e-mail message begins with
a header.
From:
To:
Date:
Subject:
9
E-mail Software Fills In
Header Information
•
•
User-friendly software hides unnecessary header
lines when displaying an e-mail message.
See the example below:
Received: from amazon.com ([208.33.217.124]) by company1.com with Microsoft
SMTPSVC(5.5.1877.447.44); Sat, 3 Jun 2000 12:14:03 -1000
Received: by amazon.com id OAA04950; Sat, 3 Jun 2000 14:28:33 -0700 (PDT)
Date: Sat, 3 Jun 2000 14:28:33 -0700 (PDT)
Message-Id: <[email protected]>
X-AMAZON-TRACK: [email protected]
X-AMAZON-TRACK-2: fathers-day-4
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary=amazon
From: Amazon.com <[email protected]>
Subject: Save $25 at Amazon.com's New Tools & Hardware Store
To: [email protected]
Return-Path: [email protected]
10
How E-mail Works
• E-mail systems follow the client
server approach.
– Cooperate to send an email message
• From sender to recipient’s mailbox
• Sender’s computer is the client
– Contacts an e-mail server program on the
recipient’s computer
– Stores the message in the recipient’s
mailbox
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Figure 20.1
Figure 20.1 An e-mail transfer across the Internet requires two programs: a
client on the sender’s computer and a server on the recipient’s computer.
Using E-mail From A Personal
Computer
• Most personal computers do not
receive e-mail directly.
– Arrange to have a mailbox on a large
computer
– Contacts the main computer system
– Obtains a copy of their mailbox
13
Mailbox Address Format
• Addresses consist of a string of
characters separated by the “@”.
• The prefix:
– identifies the user.
• The suffix:
– gives the domain name of the computer
on which the user’s mailbox resides.
14
Abbreviations Make E-mail
Friendly
•
Most e-mail systems allow a user to
define abbreviations for the mailbox
address. For example:
1. Venus.engineering.somecompany.com
becomes eng
2. Allowing the address of
jane@eng
15
Aliases Permit Arbitrary
Abbreviations
• Most commercially available
software supports an e-mail alias.
– Requires the user to prepare a list of
aliases
– Translates the alias to a longer e-mail
address
• ‘mary’ can be used in place of:
– [email protected]
16
Aliases Shared By All Users
Of A Computer System
• System-wide aliases make it
possible for all users to share
abbreviations.
– Consider these:
• Webmaster
• Listmanager
• Help
17
Sending To Multiple
Recipients
• E-mail systems allow users to
send messages to multiple
recipients.
–Specify multiple mailbox addresses
on the ‘To’ line of message
•For example:
–To: [email protected], [email protected]
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Mailing List: An Alias for
Multiple Recipients
• A mailing list is an e-mail alias
that specifies multiple recipients
• The system:
–Sends a message to the alias
–Delivers a copy to each recipient
on the list
19
Public Mailing Lists And Mail
Exploders
• A public list permits a user on any
computer connected to the Internet to
send a message to a list of recipients.
• When the e-mail message reaches the
destination computer, an exploder:
– Finds the name
– Expands the abbreviation
– Forwards a copy to each recipient
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Figure 20.2
Figure 20.2 The path of a mail message sent to a public mailing list that contains
three recipients. A Mail exploder retrieves the message, and forwards a copy to
each recipient on the list.
E-mail To And From NonInternet Sites
• E-mail can be forwarded to other
networks.
• For example, Compuserve:
– Does not use the same Internet
protocols
– Uses software on an intermediate
computer to send and receive Internet
e-mail
22
Access To Services Via
E-mail
• A computer program can:
–Be used to answer and reply to
an e-mail message.
• An e-mail message can:
–Be used to provide access to a
variety of remote services.
23
Speed, Reliability, And
Expectations
• E-mail systems are more reliable
than postal mail systems.
– Delivery is within minutes
– Notified if a message cannot be
delivered
• Not all homes have computers
connected to the Internet.
• Differences in expectations can
make e-mail frustrating.
24
Impact And Significance Of
Electronic Mail
• After using it, email benefits
become apparent.
– Combines benefits of instantaneous
communication with freedom from
interruption
– Provides a way for groups to share
common interests
– Can communicate with more people
25
Joining A Mailing List
• To join a list, the user must
send a request via e-mail.
• The request is not sent to the
list but to a second alias used
for joining or leaving a list.
26
Glossary
• Electronic Mail
•
– (E-mail) A service that permits one to
send a memo to another person, a
group, or a computer program.
Mail Alias
– A synonym for e-mail alias.
28
Glossary
• Mailbox
•
– A storage area, usually on disk, that
holds incoming e-mail messages until a
user reads the mail.
Mailbox Address
– A synonym for e-mail address.
29
Glossary
• Mailing List
•
– An electronic mail address that includes
a list of recipients.
Postmaster
– By convention, an e-mail alias for the
person who manage the electronic mail
software on a given computer.
30
Glossary
• Smiley
•
– A sequence of characters, usually
found in an e-mail message, that
indicates humorous intent. The three
character sequence :-) resembles a
smiling face turned sideways.
POP
– Abbreviation for Post Office Protocol.31