Emails on internet

7/30/2019 Emails on internet

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Hello.. ladies and gentlemen!!!


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ailE-


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ailE-

Electronic mail, or e-mail has been around for

over two decades.

has its own conventions and styles

little ASCII symbols called smileys or

emoticons in e-mail


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rotating the book 90 degrees clockwise will

make them clearer


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The first e-mail systems simply consisted of

file transfer protocols

recipient's address

1. Sending a message to a group of people was

inconvenient

2. Messages had no internal structure, making

computer processing difficult.3. The originator (sender) never knew if a message

arrived or not.

Limitations of the above approach:


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4. If someone was planning to be away on

business for several weeks and wanted all

incoming e-mail to be handled by his

secretary, this was not easy to arrange.

5. poor user interface

6. no multimedia support


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Architecture and Services

overview of what e-mail systems can do and

how they are organized

consist of two subsystems:

user agents

message transfer agents


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e-mail systems support five basic functions

Composition refers to the process of creatingmessages and answers

Transfer refers to moving messages from theoriginator to the recipient

Reporting has to do with telling the originatorwhat happened to the message

Displaying incoming messages is needed sopeople can read their e-mail

Disposition is the final step and concerns whatthe recipient does with the message afterreceiving it.


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Additional services:

mailboxes

mailing list

carbon copies blind carbon copies

high-priority e-mail

secret (i.e., encrypted) e-mail


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Key ideas:

envelope contains all the information needed

for transporting the message, such as the

destination address, priority, and security level

message:

header

body


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Envelopes and messages. (a) Paper mail. (b) Email.


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The User Agent

A program (sometimes called a mail reader)that accepts a variety of commands for

composing

receiving replying to messages

manipulating mailboxes

User agent interface: fancy menu- or icon-driven

1-character commands from the keyboard


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Sending E-mail:

the destination address

a word processing program, or possibly with a

specialized text editor built into the user agent

destination address format: user@dns-address

Most e-mail systems support mailing lists:

locally remotely


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Reading E-mail

K:read or unread

A:answered(replied)

F:forwarded

Flags: Command user interface:D:deleteK:read or unread

A:answered(replied)

F:forwarded


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Message Formats

RFC 822:

basic e-mail system using ASCII encoding

designed decades ago no clear distinction between envelope fields

and header fields

user agent builds a message and passes it tothe message transfer agent


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RFC 822 header fields related to

message transport


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Some fields used in the RFC 822

message header


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MIMEThe Multipurpose Internet Mail Extensions

Earlier e-mail systems: English and ASCII using RFC 822

Problems include sending and receiving:

1. Messages in languages with accents (e.g., French

and German). 2. Messages in non-Latin alphabets (e.g., Hebrew and

Russian).

3. Messages in languages without alphabets (e.g.,

Chinese and Japanese). 4. Messages not containing text at all (e.g., audio or

images).


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RFC 822 headers added by MIME

ASCII String

message id

Type of encoding

7 types


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MIME header, continued


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Message Transfer : SMTP

transferring the message between sender and

receiver

SMTP : simple mail transfer protocol

TCP connection to port 25 of the destination

machine

No checksums are needed because TCP

provides a reliable byte stream


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Problems with SMTP:

older implementations cannot handle

messages exceeding 64 KB

different timeouts for client and server

solution extended SMTP (ESMTP)

clients wanting to use it should send an EHLO

message instead ofHELO initially


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POP3(Post Office Protocol V3):

simple download-and-delete requirements foraccess to remote mailboxes

POP3 begins when the user starts the mail

reader TCP connection to port 110

Goes through 3 states:

Authorization

Transactions

Update


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POP3


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IMAP (Internet Message Access Protocol)

all the e-mail will remain on the server

indefinitely in multiple mailboxes

reading even parts of messages for slower

modem connections

allows for creating, destroying, and

manipulating multiple mailboxes on the server


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Comparison b/w POP3 and IMAP:


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Thank

U

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Emails on internet