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Chapter 22

Simple MailTransfer Protocol

(SMTP)

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CONTENTSCONTENTS• USER AGENT (UA)• ADDRESSES• DELAYED DELIVERY• ALIASES• MAIL TRANSFER AGENT (MTA)• COMMANDS AND RESPONSES• MAIL TRANSFER PHASES• MIME• MAIL DELIVERY • MAIL ACCESS PROTOCOLS

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Figure 22-1

SMTP concept

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Figure 22-2

UAs and MTAs

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Figure 22-3

Relay MTAs

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Figure 22-4

Mail gateway

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USERAGENT

(UA)

22.122.1

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Figure 22-5

Format

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ADDRESSES

22.222.2

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Figure 22-6

Address

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DELAYEDDELIVERY

22.322.3

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Figure 22-7

Sender-sitedelay

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Figure 22-8

Receiver-sitedelay

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ALIASES

22.422.4

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Figure 22-9

Alias expansion

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Figure 22-10

One-to-many expansion

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Figure 22-11

Many-to-oneexpansion

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MAILTRANSFER

AGENT

22.522.5

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Figure 22-12

Email system

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COMMANDSAND

RESPONSES

22.622.6

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Figure 22-13

Commands and responses

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Figure 22-14

Command format

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MAILTRANSFER

PHASES

22.722.7

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Figure 22-15

Connection establishment

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Figure 22-16

Message transfer

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Figure 22-17

Connection termination

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MULTIPURPOSEINTERNET

MAIL EXTENSIONS(MIME)

22.822.8

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Figure 22-18

MIME

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Figure 22-19

MIME header

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Figure 22-20

Base64

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Figure 22-21

Quoted-printable

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MAILDELIVERY

22.922.9

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Figure 22-22

Email delivery

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MAIL ACCESSPROTOCOLS

22.1022.10

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Figure 22-22

POP3