Name: Shwetanshu GuptaMBA- 1st Sem- 49

E- mail ?

One of the most important services of internet is electronic- mail. Electronic mail, commonly referred to as e-mail since 1993, is a method of exchanging digital messages from a user to one or more recipients.Some early email systems required both the users to be online at the same time.

Cont’d

Today's email systems are based on a store-and-forward model.

Requires an account on a mail server and supporting software on your PC

The username and password will allow you to access your account

All e-mail programs allow you to Send, Compose, Reply, and Forward mail

E-mail format

An Internet email message consists of three components: Envelope, Header and Body.

ArchitectureUser Agent -Software program that composes, reads, replies to, and forwards messages. It also handles mailboxes.

Message Transfer Agent - The actual mail transfer is done through message transfer agents. SMTP is an example of an MTA.

Message Access Agent - The software that pulls messages out of a mailbox. POP3 and IMAP4 are examples of MAAs.

SCENARIORS IN E-MAIL

When the sender and the receiver of an e-mail are on the same mail server, we need only two user agents.

When the sender and the receiver of an e-mail are on different mail servers, we need two UAs and a pair of MTAs (client and server).

When the sender is connected to the mail server via a LAN or a WAN, we need two UAs and two pairs of MTAs (client and server).

When both sender and receiver are connected to the mail server via a LAN or a WAN, we need two UAs, two pairs of MTAs (client and server), and a pair of MAAs (client and server). This is the most common situation today.

SMTP, POP 3, IMAPV4

For exchanging of e-mail, protocols are required. These are:

SMTPSMTP is short for Simple Mail Transfer Protocol. It is a standard for sending electronic mail over internet and part of the TCP/IP protocol suite.

SMTP defines the message format and the message transfer agent (MTA), which stores and forwards the mail.

SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified and then the message text is transferred.

The direction of the bulk data (messages) is from the client to the server.

SMTP ARCHITECTURE

Commands and Responses

Commands are sent from client to server; responses vice versa.

Keywords; argument(s)

Commands format

Commands14 different commands. First 5 are required by all institutions.

Next 3 are often used, but highly recommended.

Last 6 are seldom used.

Responses

Responses are3-digit codesCodes that begin with a 2 are positive completions

LIMITATIONS OF SMTP:

Security matters for SMTP are worse.Its usefulness is limited by its simplicity.Transmission of binary files using SMTP is not possible without converting into text files. Use MIME to send mail in other format.It is limited to 7-bit ASCII characters only. SMTP servers may reject mail messages beyond some specific length.

POP3 AND IMAPV4The first and the second stages of mail delivery use SMTP. However, SMTP is not involved in the third stage because SMTP is a push protocol; it pushes the message from the client to the server.

In other words, the direction of the bulk data (messages) is from the client to the server.

On the other hand, the third stage needs a pull protocol; the client must pull messages from the server. The direction of the bulk data are from the server to the client. The third stage uses a message access agent.

There are 3 stages in Mail Delivery:The first and the second stages of mail delivery use SMTP( push messages) The third stage of mail delivery use POP3 or IMAP4(pull messages)

Stages of Mail Delivery

POP3 is simple and limited in functionality.Need POP3 client on user machine and POP3 server on the mail server machine.It is a pull protocol; the client must pull messages from the server. The direction of the bulk data are from the server to the client.It is a message access agent.

Pop 3

POP 3

Pop3 has two modes: keep mode and delete modeIn delete mode mail is deleted from mailbox after each retrieval.In keep mode, mail remains in mailbox after each retrieval.

Advantages:

Simple protocolEasier to implementCopies all messages when connection is made.

Disadvantages: Don’t allow user

to organize mails on server.Don’t allow user to partially check the contents of mail before downloading.

IMAPV4

As its name implies, IMAP allows us to access email messages wherever we are . Basically, email messages are stored on servers. Whenever we heck inbox, our email client contacts the server to connect with messages. When we read an email message using IMAP, we aren't actually downloading or storing it on computer; instead, we are reading it off of the server. As a result, it's possible to email from several different devices without missing a thing.

It as an intermediary between email client and email server. When you sign into an email client like Microsoft Outlook, it contacts the email server using IMAP. The headers of all of your email messages are then displayed. If you choose to read a message, it is quickly downloaded so that you can see it - emails are not downloaded unless you need to open them.

POP works by contacting email server and downloading all new messages from it. Once they are downloaded, they disappear from the server. If we decide to check email from a different device, the messages that have been downloaded previously will not be available.POP works fine for those who generally only check their email messages from a single device; those who travel or need to access their email from various devices are much better off with IMAP-based email service.

Unlike POP, IMAP allows us to access, organize, read and sort email messages without having to download them first. As a result, IMAP is very fast and efficient. The server also keeps a record of all of the messages that we send, allowing us to access sent messages from anywhere. IMAP does not move messages from the server to computer; instead, it synchronizes the email that's on computer with the email that's on the server.

POP3 VS IMAPV4

Advantages of imapv4

A user can check the email header prior to downloadingA user can search the contents of the email for a specific string of characters prior to downloadingA user can partially download email (helpful if email contains huge attachments and connection is slow)A user can create, delete, or rename mailboxes on the mail serverA user can create a hierarchy of mailboxes in a folder for email storage

It allows us to access email messages from anywhere, and from many different devices as we want.

It only downloads a message when we click on it. As a result, you do not have to wait for all of your new messages to download from the server before you can read them.

Attachments are not automatically downloaded with IMAP. As a result, you're able to check your messages a lot more quickly and have greater control over which attachments are opened.

Finally, IMAP can be used offline just like POP - you can basically enjoy the benefits of both protocols in one.

CONCLUSIONAs the world becomes more mobile than ever, IMAP is becoming more and more popular. The proliferation of smartphones, laptops, tablets and other devices is making the demand for IMAP stronger than ever. While POP will remain popular with people who only access their email via one or two devices - and those who have slow connections to the Internet - IMAP is sure to remain the protocol of choice for most of today's busy people.