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how email works

how email works

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how email works

  1. 1. DATA COMMUNICATION TOPIC:THE WHY,WHAT AND HOW OF EMAIL Submitted by: SHRADHA KANODIA[1MS13IS102] VEERAVALLI HARIKA[1MS13IS121] M.S RAMAIAH INSTITUTE OF TECHNOLOGY
  2. 2. What is Electronic Mail? • Electronic Mail - It is a facility that allows users to transmit messages across the Internet. • It is the most widely used application service offering a fast conventional method of transferring information. • It can accommodate large messages or voluminous memos. • It allows communication between groups or single individuals.
  3. 3. HOW EMAIL IS SENT
  4. 4. MESSAGE ACCESS PROTOCOLS 1) POP3 2) IMAP
  5. 5. Post Office Protocol Version 3 (POP3) • Post Office Protocol Version 3 has been the most popular protocol has been the most popular protocol used to transfer messages from a permanent mailbox to a local computer. • When the user invokes a POP3 client, it establishes a TCP connection and contacts a POP3 server on the mailbox computer. The user sends a login and a password to authenticate the session. If login was successful, the client sends commands to retrieve copies of messages and to delete messages from the permanent mailbox. • Both SMTP servers and POP3 servers must synchronize access to the mailbox.
  6. 6. POP3 Commands • USER name: User name for authentication • PASS password: Password used for authentication • STAT: Get number and total size of message • LIST: [msg] get size of message • RETR: msg Send message to client • DELE: msg Delete message from mailbox • RSET: Cancel previous delete requests. • QUIT: Updates mailbox (deletes messages) and quits.
  7. 7. Internet Message Access Protocol (IMAP) • An alternative to POP3 is IMAP version 4. It defines an abstraction known as a MAILBOX. Mailboxes are located on the same computer as a server. • IMAP4 is a method for accessing electronic mail messages that are kept on a mail server. It permits a client e-mail program to view and manipulate those messages. • Electronic mail stored on an IMAP server can be viewed or manipulated from a desktop computer at home, a notebook computer, or at a workstation. We can also say that mail messages can be accessed from multiple locations.
  8. 8. What are the functions of IMAP4? Includes operations for: • creating mailboxes • deleting mailboxes • renaming mailboxes • checking for new messages • permanently removing messages • setting and clearing flags • searching • fetching of message attributes texts, and portions.
  9. 9. • IMAP provides extended functionality for message retrieval and processing. • Users can obtain information about a message or examine header fields without retrieving the entire message. • Users can search for a specified string and retrieve portions of a message. This is useful for slow-speed dialup connections since they wont need to download useless information.
  10. 10. MESSAGE TRANSFER AGENT (SMTP)
  11. 11. Introduction to SMTP • The TCP/IP Protocol specifies a standard for the exchange of mail between machines. This standard specifies the exact format of messages a client on a single machine uses to transfer mail to a server on another. • This standard transfer protocol is known as the Simple Mail Transfer Protocol. (SMTP) The main objective of SMTP is to provide the reliability and efficiency of mail transfer.
  12. 12. • SMTP basically focuses on how the underlying mail delivery system passes messages across an internet from machine to machine. • SMTP does not specify how the mail system accepts mail from a user or how the user interface presents messages.
  13. 13. • An important feature of SMTP is "mail relaying." Mail relaying is SMTP's capability of transporting across networks. • Through SMTP, a process can transfer mail to another process using the same or other networks via a relay process accessible to both networks. • Mail messages can be passed through a number of intermediate relay or gateways hosts from sender to ultimate destination.
  14. 14. Basic SMTP Design User File System Client SMTP Server SMTP File System
  15. 15. OPERATION Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (email) transmission. Although electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user-level client mail applications typically use SMTP only for sending messages to a mail server for relaying. For receiving messages, client applications usually use either POP3 or IMAP. A message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA). The transmission details are specified by the Simple Mail Transfer Protocol (SMTP). When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA.
  16. 16. Every time an MTA receives an email message, it adds a received trace header field to the top of the header of the message,thereby building a sequential record of MTAs handling the message. The process of choosing a target MTA for the next hop is also described in SMTP, but can usually be overridden by configuring the MTA software with specific route
  17. 17. Security Considerations
  18. 18. Mail security and spoofing • SMTP is not a secure protocol. • A user may spoof, which means they may trick the protocol to send a message posing as someone else. • Usually a user will prove that they are authentic in the message body with a digital signature or SPF (sender policy framework) records. • SPF records work by telling people which machines you send email from, and if the sender is not one of those machines then they are lying. • If relay is on, no authentication possible. • Spam was a huge problem early on because early defaults had relay on and people didn't know how to turn it off.
  19. 19. Scope of operation of SMTP servers • An SMTP server may refuse to accept mail for any operational or technical reason that makes sense to the site providing the server. • If sites take excessive advantage of the right to reject traffic, the ubiquity of email availability (one of the strengths of the Internet) will be threatened. • Considerable care should be taken and balance maintained if a site decides to be selective about the traffic it will accept and process. • In recent years, use of the relay function through arbitrary sites has been used as part of hostile efforts to hide the actual origins of mail. • Some sites have decided to limit the use of the relay function to known or identifiable sources, and implementations should provide the capability to perform this type of filtering. • When mail is rejected for these or other policy reasons, a 550 code should be used in response to EHLO, MAIL, or RCPT as appropriate.

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