Services Provided by e-mail system, components of the e-mail system.. - Cyber security & Technology


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Friday, July 20, 2018

Services Provided by e-mail system, components of the e-mail system..


An e-mail system provides five basic functions:

1.      Composition. It refers to the process of creating messages and answers. Any kind of text editor can be used for composing the body of the message.

2.      Transfer. It refers to moving messages from the sender to recipient.

3.      Reporting. It refers to ensure the confirmation of delivery of the message. Such a reporting system helps in determining whether the mail is delivered, lost or rejected.

4.      Displaying. It means presenting the message in the form the user can read. In some cases conversion or some special viewer softwares are required to present the message for e.g. in case of digitized voice.

5.      Disposition. It is the final step and concerns what the recipient does with the message after receiving it. The user can save the message, delete the message before reading it or can delete the message after reading it.


The basic component of an email system are:

1.      User Agent (UA)

2.      Message Transfer Agent (MTA)

3.      Mail box

4.      Spool file .

1.      User Agent (UA)

·        The UA is normally a program used to send and receive mail.

·        It is sometimes called a mail reader.

·        User agent accepts variety of commands for composing, receiving and replying to messages, as well as for manipulating mailboxes.

·        Some user agents provide an extra user interface with menus or icons, thus allowing window type (GUI based) interactions with the system. .

2.      Message Transfer Agent (MTA)

·        MTA are responsible for actual mail transfer from one system to another

·        To send a mail, a system must have a client MTA, and to receive mail, system must have a server MTA (see fig.).

·        MTA forwards the mails to the mailboxes of the recipients if they are connected in the same machine

·        MTA delivers the mails to peer MTA if the destination mailbox is in another . machine.

·        Such a delivery from one MTA to another is done by Simple Mail transfer Protocol (SMTP) .

·        There can also be intermediate MTAs that act as transit for transferring mails from one MTA to another.

3.      Mailbox

·        A mailbox is a special file on a local hard drive that is used collect the e- mails.

·        The delivered mails are appended in this file. The user can read and delete the mails from his mailbox file.

·        Each user must have a mailbox in order to use an-email system

·        Only the owner of the mailbox has access to it.

·        Commands are needed to create and destroy the mailboxes, inspect the content of mailboxes, insert and delete messages from mailboxes and so on.

4.       Spool file.

·        It contains the mails to be sent.

·        The User Agent (UA) appends the outgoing mails in the spool file using SMTP

·        Message Transfer Agent (MTA) extracts the pending mail from the spool file for their delivery .

·        Figure 12.1 shows the component and mechanism of flow of e-mail.

·        E-mail allows one name, an alias, to represent several different e-mail addresses. It is known as mailing list.

·        Every time a message is to be sent, the system checks the recipient's name against the alias database.

·        If there is a mailing list for the defined alias, separate messages, one for each entry in the list, must be prepared and handed to the MTA.

·        If there is no mailing list for the alias, the name itself is the receiving address and a single message is delivered to the mail transfer entity.

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