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Active In SP

Posts: 2,270
Joined: Sep 2010
13-10-2010, 05:22 PM

.ppt   IMAP_01_3.ppt (Size: 617 KB / Downloads: 83)

Kusum Lata
Vikas Srivastava
Sandeep Goutele
Rohit Mishra

POP3 Post Office Protocol (Version 3 )


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
Similar to SMTP command/reply lockstep protocol.
Used to retrieve mail for a single user
requires authentication
Commands and replies are ASCII lines.
Replies start with “+OK” or “-ERR”.
Replies may contain multiple lines.

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
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.
TOP - send header lines from messages.
APOP - alternative authentication
message digest based on opening greeting sent from POP server.
Requires shared secret!
No cleartext password on the network.
Does not authenticate the server!!!!

What is spam

Spam filtering methods
access control method
authentication method
content based filtering method


PEMF achieves three design goals.
High efficiency and stability

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

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..
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

IMAP Internet message access Protocol

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

Procedure of the imap protocol

All emails are kept on a mail server
Treat as local directory
work directly on server
different folders
download message headers and later on the full messages
communication procedure:
Connection initialization
Welcome of the server
Interaction between client and server
Connection closed

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

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)
Logout, Closed

Flags message attributes

List of token associated with the message that is sent by the server
A flag can be permanent or session-only
System flag:
• flag name that is pre-defined in the imap specification
• All system flags begin with ‘\’
• A keyword is defined by the server implementation
• Keywords do not begin with ‘\’


Important Note..!

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