| Introduction E-mail
(electronic mail) is the exchange of computer-stored messages by telecommunication. (Some
publications spell it email; we prefer the currently more established spelling of e-mail.)
E-mail messages are usually encoded in ASCII text. However, you can also send non-text
files, such as graphic images and sound files, as attachments sent in binary streams.
E-mail was one of the first uses of the Internet and is still the most popular use. A
large percentage of the total traffic over the Internet is e-mail. E-mail can also be
exchanged between online service provider users and in networks other than the Internet,
both public and private. E-mail can be distributed to lists of people as well as to
individuals. A shared distribution list can be managed by using an e-mail reflector. Some
mailing lists allow you to subscribe by sending a request to the mailing list
administrator. A mailing list that is administered automatically is called a list server.
E-mail is one of the protocols included with the Transport Control Protocol/Internet
Protocol (TCP/IP) suite of protocols. A popular protocol for sending e-mail is Simple Mail
Transfer Protocol and a popular protocol for receiving it is POP3. Both Netscape and
Microsoft include an e-mail utility with their Web browsers.
How Does E-mail work?
Billions of electronic mail (e-mail) messages move across the Internet every year.
Sending electronic letters, pictures and data files, either across a building or across
the globe, has grown so popular that it has started to replace some postal mail and
telephone calls. This universal medium is no longer restricted to exchange of simple text
messages and is now regularly used to deliver voice mail, facsimiles and documents that
may include images, sound and video.
Typically, a message becomes available to the recipient within seconds after it is
sent—one reason why Internet mail has transformed the way that we are able to
communicate.
1 MESSAGE SENDER uses mail software, called a
client, to compose a document, possibly including attachments such as tables, photographs
or even a voice or video recording. System software, called Transmission Control Protocol
(TCP), divides the message into packets and adds information about how each packet should
be handled-for instance, in what order packets were transmitted from the sender. Packets
are sent to a mail submission server, a computer on the internal network of a company or
an Internet service provider.
2 INTERNET MAIL ADDRESSES attached to each message are in the form "mailbox@domainname" - one specific example
being "webmaster@seniorindian.com." The
multipart domain name in the above example denotes a top-level domain (".com")
following the second-level domain ("seniorindian"). A message is delivered to an
individual or a group by the mailbox name ("webmaster").
3 MAIL SUBMISSION SERVER converts the domain name of the recipient’s mail address
into a numeric Internet Protocol (IP) address. It does this by querying domain name
servers interspersed throughout the Internet. For example, the mail submission server can
first request from the "root" name server the whereabouts of other servers that
store information about ".com" domains (a). It can then interrogate the
".com" name server for the location of the specific "sciam.com" name
server (b). A final request to the "sciam.com" name server provides the IP
address for the computer that receives the mail for sciam.com, which is then attached to
each message packet (c).
4 ROUTERS dispersed throughout the Internet read the IP address on a packet and
relay it toward its destination by the most efficient path. (Because of fluctuating
traffic over data lines, trying to transmit a packet directly to its destination is not
always the fastest way.) The packets of a single message may travel along different
routes, shuttling through 10 or so routers before their journey’s end.
5 DESTINATION MAIL SERVER places the packets in their original
order, according to the instructions contained in each packet, and stores the message in
the recipient’s mailbox. The recipient’s client software can then display the
message. |
