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POP3 & IMAP. - [email protected] - 10-04-2017 [attachment=5928] POP3 & IMAP By: Kusum Lata Vikas Srivastava Sandeep Goutele Rohit Mishra POP3 Post Office Protocol (Version 3 ) 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 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 PEMF achieves three design goals. Universality Transparency 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 Functionality: Treat as local directory work directly on server copy delete 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) Non-Authenticated Authenticated Selected 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 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 \ |