Tiểu luận môn mạng máy tính Electronic Mail: SMTP

Tiểu luận môn mạng máy tính Electronic Mail: SMTP To explain the architecture of electronic mail using four scenarios. To explain the user agent (UA) Transfer Protocol (SMTP) as the formal protocol that handles MTA. To explain email transfer phases.

Presented by: Pham Van Chi

Bui Thi The Ha

Electronic Mail: SMTP

 To explain the architecture of electronic mail using four scenarios.

 To explain the user agent (UA)

 Transfer Protocol (SMTP) as the formal protocol that handles MTA.

 To explain e-mail transfer phases.

Explain the architecture of electronic mail

To explain the architecture of email, we give four scenarios

Scenarior 1

Scenarior 2

Scenarior 3

Scenarior 4

Figure 1 First scenario

1

2

When the sender and the receiver of an

e-mail are on the same e-mail server,

we need only two user agents.

Note:

Figure 2 Second scenario

1

5

When the sender and the receiver of an

e-mail are on different e-mail servers,

we need two UAs and a pair of MTAs

(client and server).

Note:

Figure 3 Third scenario

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:

Figure 4 Fourth scenario

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:

Figure 5 Push versus pull

Explain the user agent (UA),

- UA là thành ph n ầ đầ u tiên c a m t h th ng th i n t ủ ộ ệ ố ư đ ệ ử

- Cung c p d ch v t i ng ấ ị ụ ớ ườ ử ụ i s d ng

- Giúp quá trình g i nh n th d dàng h n ử ậ ư ễ ơ

Figure 6 User agent

Some examples of command-driven user agents are mail ,

pine , and elm

Note:

Transfer Protocol (SMTP)

- Để ử g i mail, h th ng ph i có client MTA ệ ố ả

- Để ậ nh n mail H th ng ph i có server MTA ệ ố ả

- 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

- Scenario 4 là tr ườ ng h p th ợ ườ ng g p nh t ặ ấ

Figure 7 SMTP range

Figure 8 Commands and responses

• 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

Figure 9 Message transfer

Figure 10 Connection termination

2

221 service closed

Send A Fake Mail uses QK SMTP server

-Sử dụng TELNET để login cổng 25 (the well-known port for SMTP)

- Sử dụng câu lệnh để gửi email

- Giả sử billg@microsoft.com gửi 1 email cho chipvc@gmail.com

Example

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: billg@microsoft.com

250 billg@microsoft.com Address Okay (Server gives a positive response)

RCPT TO: chipvc@gmail.com

250 chipvc@gmail.com Address Okay

=================== Header and Body ==================

DATA (type this command to start input data)

354 Please start mail input

From:Gates <billg@microsoft.com>

Figure 11 SMTP, Pop3 and IMAP4

Any