INTRODUCTION OF E-MAIL
Electronic mail, most commonly referred to as email or e-mail since ca. 1993, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the same time, in common with instant messaging. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to a mail server, for as long as it takes to send or receive messages.
with E-mail, sending and receving messages has become an easy task. it simply involves opening of a connection for communication, sending data finally closing down the connection.
THE BENEFITS OF E-MAIL
it is used frequently in our day to day activities.businesses depend upon email to update their customer database, pian and manufacture their output etc.tody,people even use mobile phones and PDA'S to work with e-mail.
Different parts of the mailing system communicate with each other in defined message formats and rules called protocols. There are numerous standard protocols defined, out of which a few important ones are.
Simple Mail Transfer Protocol (SMTP):
SMTP and its modern form Enhanced SMTP are used by an MUA to talk to the MTAs and by the MTAs to talk amongst themselves. It is the most widespread protocol used for mailing purposes and is defined in RFC-5321 and 5322. It is a simple text based protocol in which the sender communicates with the receiver by issuing command strings over a TCP connection. A single transaction may consist of command sequences like MAIL (to establish Return Path) ->RCPT (To establish recipients) ->DATA (To send message header and body). The replies to such commands may be intermediate replies for DATA which may be positive replies, negative replies or even permanent failure replies.
Post Office Protocol (POP):
Also known as POP3, it is used between a MUA and MAA and is defined in RFC-1939. Being cheap and simple, it is popular among ISPs. Here, a username and password is sent following which, entire mailbox can be downloaded to the MUA. This has only one option, either to retain the mails on the server or to delete them after downloading.
Internet Message Access Protocol (IMAP):
This is yet another protocol used between a MUA and MAA. It is more powerful and flexible than a POP, but is more taxing on the ISPs in resource count. It allows selective message downloading and deleting among many other features. It is defined by RFC-3501. The mail programs used to drop the 8th bit of every byte to attain 12.5% speed up. This however couldn’t be used when formats like GIFs and binary files were sent as attachments. Thus another protocol Multipurpose Internet Mail Extensions (MIME) was developed for the same which provided for the styled text wherein the body of the message was split into several parts by MIME separator strings and each part was separately encoded and decoded. MIME is invisible to MAA, MDA and MTAs. But it is almost obsolete since users started using HTML for emails.