short notes on SMPT (simple mail transfer protocol), POP3 ( post office protocol3) and IMAP (internet mail access protocol) with the help of diagram

SIMPLE MAIL TRANSFER PROTOCOL (SMTP):-

• SMTP is at the heart of Internet electronic mail. SMTP transfers messages from senders' mail servers to the recipients' mail servers.
• SMTP is a delivery protocol only. It cannot pul l messages from a remote server on demand. Other protocols, such as the Post Office Protocol (POP) and the Internet Message Access Protocol (IMAP) are specifically designed for retrieving messages and managing mail boxes. However, the SMTP protocol has a feature to initiate mail queue processing on a remote server so that the requesting system may receive any messages destined for it.
• SMTP is a "push" protocol that does not allow one to "pull" messages from a remote server on demand. To do this a mail client must use POP3 or IMAP. 

In order to send mail, the mail server software uses SMTP, or Simple Mail Transfer

Protocol. Here is how SMTP works:-

•The mail client, which is the software used to compose the e-mail (like Outlook

Express), will send the mail to the mail server that is configured in the mail client

software package. The mail server’s address can be found under the SMTP server

configuration.

•The SMTP server will analyze the “To”, “CC”, and “BCC” addresses to determine

which server or servers the e-mail is supposed to go.

•Finally, the SMTP server will send the e-mail to the destination mail server or

servers.

POP3 (post office PROTOCOL3):-

• POP3 progresses through three phases: authorization, transaction and update.

In order to receive mail, the mail server software will use either POP3 - Post Office

Protocol 3, or IMAP - Internet Message Access Protocol. Here is how POP3 works:

• The POP3 server will receive the e-mail from an SMTP server.

• The POP3 server will analyze the “To”, “CC”, and “BCC” addresses to determine where it is supposed to go.

• The POP3 server will send the mail to the “inbox” for that address (if the e-mail address is a legitimate address for that domain). If the address is not a legitimate address for that domain, the POP3 server will send an error message back to the SMTP server.
• When the user opens his/her mail client (like Outlook Express), the software package will check the POP3 server for new mail. The mail server’s address can be found under the POP3 server configuration.

• The design of POP and its procedures supports end-users with temporary Internet
• connections, such as dial-up access, allowing these users to retrieve e-mail when connected and then to view and manipulate the retrieved messages when offline.
• Although most clients have an option to leave mail on server, e-mail clients using POP generally connect, retrieve all messages, store them on the user's PC as new messages, delete them from the server, and then disconnect.

IMAP (Internet Mail Access Protocol ):-

• IMAP (Internet Mail Access Protocol). provide multi-folder of messages facility.
• IMAP is a newer protocol used for receiving e-mail, and a number of mail server software packages are using this protocol rather than POP3 to receive mail.
• A newer function of some mail server packages is Mail Filtering. These are mail servers that act as “spam detectors”. A “spam detector” analyzes the incoming mail and determines whether the mail is “spam” (junk e-mail) or not. The factors to determine whether the mail is “spam” can vary based on the package. Some common factors used are: keywords, the domain from which the mail originated, and letter combinations.