SMTP Email Sistem [Compatibility Mode]

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Upon completion you will be able to:

Electronic Mail:

SMTP, POP, and IMAP

Objectives

Upon completion you will be able to:

•

Understand four configurations of email architecture

•

Understand the functions and formats of a user agent

•

Understand MIME and its capabilities and data types

•

Understand the functions and commands of an MTA

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20.1 ARCHITECTURE

To

To explainexplain thethe architecturearchitecture ofof email,email, wewe givegive fourfour scenariosscenarios.. WeWe beginbegin with

with thethe simplestsimplest situationsituation andand addadd complexitycomplexity asas wewe proceedproceed.. TheThe fourthfourth scenario

scenario isis thethe mostmost commoncommon inin thethe exchangeexchange ofof emailemail..

The topics discussed in this section include: The topics discussed in this section include:

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[image:3.842.218.588.209.375.2]

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When the sender and the receiver of

an email are on the same system, we

need only two user agents.

Note:

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[image:5.842.64.745.82.442.2]

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When the sender and the receiver of

an email are on different systems, we

need two UAs and a pair of MTAs

Note:

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[image:7.842.79.700.61.529.2]

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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

Note:

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[image:9.842.93.719.100.526.2]

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[image:10.842.108.680.80.456.2]

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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

Note:

or a WAN, we need two UAs, two pairs

of MTAs (client and server), and a pair

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20.2 USER AGENT

The

The useruser agentagent (UA)(UA) providesprovides serviceservice toto thethe useruser toto makemake thethe processprocess ofof sending

sending andand receivingreceiving aa messagemessage easiereasier..

Services Provided by a User Agent Services Provided by a User Agent User Agent Types

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[image:13.842.82.736.88.352.2]

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Some examples of command-driven

user agents are

mail

,

pine

, and

elm

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Some examples of GUI-based user

agents are

Eudora

,

Outlook

, and

Netscape

.

Note:

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[image:16.842.199.735.116.537.2]

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[image:18.842.96.686.100.472.2]

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[image:19.842.147.633.135.400.2]

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[image:20.842.110.735.163.393.2]

Table 20.1

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[image:21.842.113.731.107.442.2]

Table 20.1

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[image:22.842.114.703.113.344.2]

Table 20.2

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[image:23.842.103.701.134.504.2]

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[image:24.842.88.758.127.457.2]

Table 20.3

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[image:25.842.96.717.142.470.2]

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20.3 MESSAGE TRANSFER AGENT:

SMTP

The

The actualactual mailmail transfertransfer requiresrequires messagemessage transfertransfer agentsagents (MTAs)(MTAs).. TheThe protocol

protocol thatthat definesdefines thethe MTAMTA clientclient andand serverserver inin thethe InternetInternet isis calledcalled Simple

Simple MailMail TransferTransfer ProtocolProtocol (SMTP)(SMTP)..

Commands and Responses Commands and Responses Mail Transfer Phases

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[image:27.842.97.739.172.417.2]

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[image:30.842.223.610.65.527.2]

Table 20.4

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[image:31.842.199.663.63.526.2]

Table 20.5

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[image:32.842.136.710.49.492.2]

Table 20.5

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[image:33.842.159.627.144.384.2]

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[image:34.842.266.598.84.556.2]

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[image:35.842.171.632.147.366.2]

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$ telnet mail.adelphia.net 25

Let us see how we can directly use SMTP to send an email and simulate the commands and responses we described in this section. We use TELNET to log into port 25 (the well-known port for SMTP). We then use the commands directly to send an email. In this example, forouzanb@adelphia.net is sending an email to himself. The first few lines show TELNET trying to connect to the adelphia mail server.

$ telnet mail.adelphia.net 25

Trying 68.168.78.100...

Connected to mail.adelphia.net (68.168.78.100).

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================== Connection Establishment ================

220 mta13.adelphia.net SMTP server ready Fri, 6 Aug 2004 . . .

HELO mail.adelphia.net

250 mta13.adelphia.net

===================== Envelope ===================

MAIL FROM: forouzanb@adelphia.net

250 Sender <forouzanb@adelphia.net> Ok 250 Sender <forouzanb@adelphia.net> Ok

RCPT TO: forouzanb@adelphia.net

250 Recipient <forouzanb@adelphia.net> Ok

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

DATA

354 Ok Send data ending with <CRLF>.<CRLF>

From: Forouzan TO: Forouzan

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============= Connection Termination===============

250 Message received: adelphia.net@mail.adelphia.net

QUIT

221 mta13.adelphia.net SMTP server closing connection

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20.4 MESSAGE ACCESS AGENT:

POP AND IMAP

The

The thirdthird stagestage ofof mailmail deliverydelivery usesuses aa messagemessage accessaccess agentagent;; thethe clientclient must

must pullpull messagesmessages fromfrom thethe serverserver.. CurrentlyCurrently twotwo messagemessage accessaccess protocols

protocols areare availableavailable:: PostPost OfficeOffice Protocol,Protocol, versionversion 33 (POP(POP33)) andand Internet

Internet MailMail AccessAccess Protocol,Protocol, versionversion 44..

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[image:40.842.99.744.196.442.2]

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[image:41.842.186.655.75.527.2]

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20.5 WEB-BASED MAIL

Some

Some websiteswebsites suchsuch asas HotmailHotmail andand YahooYahoo provideprovide emailemail serviceservice toto anyone

anyone whowho accessesaccesses thethe sitesite.. MailMail transfertransfer andand retrievalretrieval requiresrequires thethe useuse of