pop3 and imap protocol

POP3 & IMAP

By:

Kusum Lata

Vikas Srivastava

Sandeep Goutele

Rohit Mishra

110/08/2010

POP3 & IMAP

POP3 Post Office Protocol

(Version 3 )

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Introduction

What is POP ?

Why POP3 came into picture?

How it works?

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Terminology used…

User Agent: end-user mail program Message Transfer Agent: responsible

for communicating with remote hosts and transmitting/receiving email (both a client and server).

Mail Exchanger: host that takes care of email for a domain.

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POP3

protocol for receiving e-mail client/server protocol achieves transparent connection between

email server and e-mail client store-and-forward service listens on well-known port 110

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POP3 contd………….

Similar to SMTP command/reply lockstep protocol.

Used to retrieve mail for a single userrequires authentication

Commands and replies are ASCII lines.Replies start with “+OK” or “-ERR”.Replies may contain multiple lines.

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POP3 – Post Office Protocol

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to establish a TCP connection

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Contd………..

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Contd……

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POP-3 Commands USER - specify username PASS - specify password STAT - get mailbox status

number of messages in the mailbox. LIST - get a list of messages and

sizes.One per line, termination line contains

‘.’ only.RETR - retrieve a message

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More POP-3 Commands

DELE - mark a message for deletion from the mailbox.

NOOP - send back positive reply RSET - reset. All deletion marks are

unmarked. QUIT - remove marked messages and

close the (TCP) connection.

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Optional Commands

TOP - send header lines from messages.

APOP - alternative authenticationmessage digest based on opening

greeting sent from POP server.Requires shared secret!No cleartext password on the network.Does not authenticate the server!!!!

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A Pop3 Exchange

> telnet monte pop3Trying 128.213.8.110...Connected to monte.cs.rpi.edu (128.213.8.110).Escape character is '^]'.+OK POP3 monte.cs.rpi.edu v7.59 server readyuser joe+OK User name accepted, password pleasepass joepw+OK Mailbox open, 1 messagesstat+OK 1 412list+OK Mailbox scan listing follows1 412.

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POP3 Proxy Platform for E-mail Filtering

What is spam? Spam filtering methods

access control method authentication method content based filtering method

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PEMF

PEMF achieves three design goals.

Universality Transparency High efficiency and stability


Work flow of PEMF


Advantages of POP3:

You can read your mail without being logged onto the Internet.

You may compose new messages to send to others without being logged onto the Internet.

Opening attachments is a quick and painless. There is not a maximum size on your mailbox. There is no advertising when you read your email All messages are stored on your hard drive

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Disadvantages of POP3:

Opening attachments is a quick and painless process, unless the attachment has a virus payload in it.

If you have JavaScript enabled in your email reader, you might be target of rogue JavaScript embedded in an email.

All messages are stored on your hard drive eating up what is sometimes very valuable space..

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Disadvantages contd………

Since all attachments are stored (downloaded) on your PC there is a potential danger of virus attack if they are not properly scanned by virus scanners.

Email folders can become corrupted and sometimes lost forever. Recovering is often a painful exercise.

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IMAP

Internet message access Protocol

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About IMAP

Internet message access protocol 1986, Stanford University Stands for accessing electronic mail that

are kept on a server access messages from more than one

computer More than one user Imap protocol based on a TCP connection

(port 143) No functionality to send messages (realized

with SMTP)

POP V/s IMAP

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Advantages over POP

Built in extension mechanism Multiple clients connected

simultaneous to the same mailbox Access to MIME Message State Information Multiple mailbox on the server Server Aid searches

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Procedure of the imap protocol

All emails are kept on a mail server Functionality:

Treat as local directory work directly on server copy delete different folders

download message headers and later on the full messages

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Procedure of the imap protocol [2]

communication procedure:Connection initializationWelcome of the serverInteraction between client and serverConnection closed

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Interaction between client and server

Client sends data - server receives: client-command begins with alphanumeric string

(‘tag’) e.g. A001 which is created for every new command

then the command with corresponding arguments follows

Server sends data – client receives Server receives and works with the command Returns the same tag with a state (OK/NO/BAD) Additional information begin with ‘*’ (untagged) Untagged in formation can be sent at every time

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Different states of an imap session

Most commands are only valid in special states (otherwise: protocol error)

4 states (initialization is not an own state) Non-Authenticated Authenticated Selected Logout, Closed

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State diagram

Reject con.

Initialization

Non-Authenticated

Authenticated

Selected

Logout,

Clo

se

Logout

Logout

Logout

Preauth

Select Close

Login

Connect

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Flags message attributes

List of token associated with the message that is sent by the server

A flag can be permanent or session-only types:

System flag:• flag name that is pre-defined in the imap

specification • All system flags begin with ‘\’

Keywords:• A keyword is defined by the server implementation• Keywords do not begin with ‘\’

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Flags Message Attributes [2]

\Seen (Message has been read) \Answered (Message has been answered) \Flagged (Message is "flagged" for

urgent/special attention) \Deleted (Message is "deleted" for removal by

later EXPUNGE) \Draft (Message has not completed

composition (marked as a draft)) \Recent (Message is "recently" arrived in this

mailbox. This session is the first session to have been notified about this message)

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Commands

LOGIN username password SELECT mailbox-name CREATE new-mailbox-name DELETE mailbox-name RENAME old-name new-name AUTHENTICATE CLOSE SEARCH COPY

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Imap sessionS: * OK IMAP4rev1 Service ReadyC: a001 login rohit zealousS: a001 OK LOGIN completedC: a002 select inboxS: * 18 EXISTSS: * FLAGS(\Answered\Flagged\Deleted\Seen\Draft)S: * 2 RECENTS: * OK [UNSEEN 17] Message 17 is the first unseen

messageS: * OK [UIDVALIDITY 3857529045] UIDs validS: a002 OK [READ-WRITE] SELECT completedC: a003 fetch 12 body[header]S: * 12 FETCH (BODY[HEADER] {350}S: Date: Wed, 11 August 2010 02:23:25 -0700 (PDT)S: From: rohit <[email protected]>S: Subject: weekend planning

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Imap session [2]

S: To: rahul <[email protected]>S: cc: bharat <[email protected]>S: Message-Id: <[email protected]>S: MIME-Version: 1.0S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCIIS:S: )S: a003 OK FETCH completedC: a004 store 12 +flags \deletedS: * 12 FETCH (FLAGS (\Seen \Deleted))S: a004 OK +FLAGS completedC: a005 logoutS: * BYE IMAP4rev1 server terminating connectionS: a005 OK LOGOUT completed

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Thank you for your attention!

pop3 and imap protocol

Technology

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