By Uthman Akinbola
E-mail which stands for electronic mail, often spelt email or e-mail,
is a method of composing, sending, storing, and receiving messages via a
network of computer systems.
It is a form of sending and receiving electronic messages in a way similar
to the mailing of letters or memos.
E-mail systems can be
administered over the entire internet, and thus we have internet e-mail, or via
an intranet. It provides an immediate (almost instantaneous) exchange of
information at very little cost. It is a widely used form of communication in
the world of today.
There are two kinds of internet e-mail
systems. These are:
(i) E-mail Client System
(ii) Webmail System
The E-mail Client System
This system makes use of a Mail
User Agent, MUA, which is called an e-mail
client. The e-mail client is an application software (computer program)
that helps maintain and manage e-mails. Examples of e-mail client are Microsoft
Office Outlook (commonly called Microsoft outlook), Microsoft Outlook Express,
Mozilla Thunderbird, Windows Mail and Windows Live Mail released in November
2007.
In this system, one's mail can be
accessed and stored on one's computer using the e-mail program. This allows
access to (stored) mails even when not online.
The client needs to be configured
for e-mail use. The program settings require the username, password, e-mail
address, incoming mail server and outgoing mail server.
There are two forms of the e-mail
client system. The first one is the common pull
e-mail, which is the traditional
e-mail system. The other is the push
e-mail.
Traditional E-mail
Traditional e-mail system is
pull-based. This means that at login (and at defined intervals while still
logged in) the e-mail client seeks to retrieve new mails i.e seeks to pull new
mails from wherever it is stored.
To show the working of this
system, let us itemise the steps involved in the case of Mr A sending a message
to his friend, Mr B.
1. Mr A, the sender, starts its e-mail program and types the
message.
2. The e-mail program
sends message, using the Simple Mail Transfer Protocol (SMTP), to the local
mail exchange server, SA, run by the e-mail service provider of Mr A.
3. SA looks at
the destination address (username@domain name) of the message and sends it to a
mail exchange server, SB, which handles messages with such address. This
mail server, SB is operated by the mail service provider of the
recipient, Mr B.
4. SB delivers
the message to the mailbox of B (a remote storage space reserved for B's
e-mails)
5. Mr B starts his e-mail
computer program and it retrieves the mail (message from A) from the mail box
using the Post Office Protocol (POP3) or the Internet Mail Access Protocol
(IMAP) depending on the kind of server operated by B's e-mail service provider.
It is important to note that the
last step is pull-based, which means, as explained earlier, that the e-mail
program pulls new messages from the remote mailbox.
The mail exchange server, mail
server for short, comprises the Mail Transfer Agent (MTA) and the Mail Delivery
Agent (MDA).
Note that:
With POP3 Mr B has access to
download messages one at a time and can only delete them from the remote
mailbox after they have been successfully saved on local storage. It is however
possible to leave the message in the mailbox in the remote storage, but there
is no provision for flagging any message as seen, answered or forwarded. Thus
POP3 is not too convenient or effective for accessing mails from different
machines or e-mail programs.
IMAP would allow Mr B to keep
messages in the remote mailbox, leaving them flagged as appropriate.
Push E-mail
For push e-mail, the last (fifth)
step above which is the delivery step, is not pull-based, it is rather
push-based.
We noted that e-mail client
retrieves (pulls) new mails from the remote mailbox traditionally, but in push
e-mail system, a new mail is pushed (delivered) to a client.
In other words, a push e-mail
process goes through the steps 1-4 highlighted above, but differs in the last
step only. The last step is different in that a special system, attached to the
traditional e-mail arrangement, monitors the remote mailbox for a new mail. It
retrieves such a mail and pushes it to the client.
Most of the push e-mail clients
are smart phones.
Webmail System
Webmail is a web-based e-mail service.
It refers to an e-mail service that is intended to be primarily accessed via a
web browser. Examples are Yahoo! Mail, Gmail (Google mail), AOL Mail, and
Windows Live Hotmail.
Among these mentioned (and popular)
webmail services, Gmail is the most recent.
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