POP3 & IMAP.
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13-10-2010, 05:22 PM
IMAP_01_3.ppt (Size: 617 KB / Downloads: 81)
POP3 & IMAP
POP3 Post Office Protocol (Version 3 )
protocol for receiving e-mail
achieves transparent connection between email server and e-mail client
listens on well-known port 110
Similar to SMTP command/reply lockstep protocol.
Used to retrieve mail for a single user
Commands and replies are ASCII lines.
Replies start with “+OK” or “-ERR”.
Replies may contain multiple lines.
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
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.
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
download message headers and later on the full messages
Welcome of the server
Interaction between client and server
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)
Flags message attributes
List of token associated with the message that is sent by the server
A flag can be permanent or session-only
• 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 ‘\’
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