school of electronics and telecommunications 1/25 presented by: pham van chi bui thi the ha...

School of Electronics and Telecommunications 1/25

Presented by: Pham Van ChiBui Thi The Ha

Electronic Mail: SMTP


OBJECTIVES:OBJECTIVES:

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 scenariosTo 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 mail server,

we need only two user agents.

Note:Note:


Figure 2 Second scenario

1

2 3 4

5


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:


Figure 3 Third scenario

1

2

3

45 6

7


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:


Figure 4 Fourth scenario

1

2

3

4 5 6

8

9


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:


Figure 5 Push versus pull


Explain the user agent (UA),

- UA là thành phần đầu tiên của một hệ thống thư điện tử

- Cung cấp dịch vụ tới người sử dụng

- Giúp quá trình gửi nhận thư dễ dàng hơn


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:


Transfer Protocol (SMTP)

- Để gửi mail, hệ thống phải có client MTA

- Để nhận mail. Hệ thống phải có server MTA

- Giao thức định nghĩa MTA client và server trên Internet

được gọi là SMTP (Simple Mail Transfer Protocol)

- Scenario 4 là trường hợp thường gặp nhất

- Hình 7 thể hiện phạm vi sử dụng giao thức SMTP trong

scenario này


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

1 QUIT

2221 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 [email protected] gửi 1 email cho

[email protected]

ExampleExample


ExampleExample 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: [email protected] 250 [email protected] Address Okay (Server gives a positive response)RCPT TO: [email protected]

250 [email protected] Address Okay =================== Header and Body ==================DATA (type this command to start input data) 354 Please start mail inputFrom:Gates <[email protected]>To:[email protected]:Sat Jan 5,2008 9:45 PMSubject:Test to send fake email


Figure 11 SMTP, Pop3 and IMAP4


Any

school of electronics and telecommunications 1/25 presented by: pham van chi bui thi the ha...

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smtp slide

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