Tiểu luận môn mạng máy tính Electronic Mail: SMTP

School of Electronics and Telecommunications
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Presented by: Pham Van Chi
Bui Thi The Ha
Electronic Mail: SMTP
School of Electronics and Telecommunications
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OBJECTIVES:
OBJECTIVES:

To explain the architecture of electronic mail using four scenarios.
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To explain the user agent (UA)

Transfer Protocol (SMTP) as the formal protocol that handles MTA.

To explain e-mail transfer phases.
School of Electronics and Telecommunications
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Explain the architecture of electronic mail
To explain the architecture of email, we give four scenarios
To explain the architecture of email, we give four scenarios

Scenarior 1
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Scenarior 2
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Scenarior 3
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Scenarior 4
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Figure 1 First scenario
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2
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When the sender and the receiver of an e-
mail are on the same mail server,
we need only two user agents.
Note:
Note:
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Figure 2 Second scenario
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5
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When the sender and the receiver of an e-
mail are on different mail servers,
we need two UAs and a pair of MTAs
(client and server).
Note:
Note:
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Figure 3 Third scenario

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7
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When the sender is connected to the mail
server via a LAN or a WAN, we
need two UAs and two pairs of MTAs
(client and server).
Note:
Note:
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Figure 4 Fourth scenario
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When both sender and receiver are
connected to the mail server via a LAN or a

WAN, we need two UAs, two pairs of MTAs
(client and server), and a pair of MAAs
(client and server). This is the most
common situation today.
Note:
Note:
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Figure 5 Push versus pull
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Explain the user agent (UA),
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UA là thành ph n u tiên c a m t h th ng th i n tầ đầ ủ ộ ệ ố ưđệ ử
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Cung c p d ch v t i ng i s d ngấ ị ụ ớ ườ ử ụ
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Giúp quá trình g i nh n th d dàng h nử ậ ư ễ ơ
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Figure 6 User agent
Some examples of command-driven user agents are mail,
pine, and elm
Some examples of GUI-based user agents are Eudora,
Outlook, and Netscape
Note:
Note:
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Transfer Protocol (SMTP)

- g i mail, h th ng ph i có client MTAĐể ử ệ ố ả
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nh n mail. H th ng ph i có server MTAĐể ậ ệ ố ả
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Giao th c nh ngh a MTA client và server trên Internet ứ đị ĩ
c g i là SMTP (Simple Mail Transfer Protocol)đượ ọ
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Scenario 4 là tr ng h p th ng g p nh tườ ợ ườ ặ ấ
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Hình 7 th hi n ph m vi s d ng giao th c SMTP trong ể ệ ạ ử ụ ứ
scenario này
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Figure 7 SMTP range
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Figure 8 Commands and responses
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command/response interaction
– commands: ASCII text
– response: status code and phrase
•
messages must be in 7-bit ASCII
•
Uses CRLF.CRLF to determine end of message
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School of Electronics and Telecommunications

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Figure 9 Message transfer
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Figure 10 Connection termination
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QUIT
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221 service closed
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Send A Fake Mail uses QK SMTP server
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Sử dụng TELNET để login cổng 25 (the well-known port for
SMTP).
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Sử dụng câu lệnh để gửi email.
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Giả sử gửi 1 email cho
Example
Example
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Example
Example Continued
================== Connection Establishment ================
220 Welcome to QK SMTP Server 3
helo hacker (Type helo & any name followed by space)
250 Hello hacker (Server Welcomes You)

===================== Envelope ===================
MAIL FROM:
250 Address Okay (Server gives a positive
response)
RCPT TO:
250 Address Okay
=================== Header and Body ==================
DATA (type this command to start input data)
354 Please start mail input
From:Gates <>
To:
Date:Sat Jan 5,2008 9:45 PM
Subject:Test to send fake email
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Figure 11 SMTP, Pop3 and IMAP4
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Any