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An Explanation of Internet Terminology

What do the parts of an e-mail address mean?
E-mail addresses normally consist of lowercase letters and numbers with no spaces. An example of such an address is:

The first part of the address ("webmaster" in the above example) identifies a unique user on a given mail server. Following the "@" symbol is the host name ("" in the above example), and it identifies the mail server on which the user's account resides. The three-letter suffix at the end of the host name and separated by a "." (pronounced "dot") identifies the type of organization operating the server. The most common suffixes are: .com (commercial), .net (networking), .org (noncommercial), .edu (educational), .gov (government), and .mil (military). Addresses outside of the United States sometimes use a two-letter suffix that identifies the country where the server is located. Some examples are: .jp (Japan), .nl (The Netherlands), .uk (United Kingdom), .ca (Canada), and .tw (Taiwan).

What is SMTP?
SMTP stands for Simple Mail Transfer Protocol. It is a special set of communications standards that allows e-mail messages to be sent across the Internet. With SMTP, mail can be sent from server to server, but POP3 is required for the recipient to have access to his incoming messages.

What is POP3?
POP3 stands for Post Office Protocol 3, and it consists of standards that allow users to retrieve e-mail from a server. When e-mail is sent to a user via SMTP, it is stored on the server until accessed by that user. Once the user logs on to his account, the POP3 protocol is used to transmit the stored mail from the server to a local mailbox, which is located on the user's computer. In short, SMTP facilitates the sending of e-mail from server to server over the Internet while POP3 allows the recipient of that e-mail to download the message to his computer and view it.

What is MIME?
MIME (Multipurpose Internet Mail Extensions) is a special extension to SMTP that allows users to send a variety of file types via e-mail. For example, the transmission of attachments such as audio and video files, images, and applications is made possible through the use of MIME. SMTP by itself only supports the transmission of ASCII text files.

What is an IP address?
An IP address is a number that is used to identify a physical point on the Internet. The IP address consists of two distinct parts: a network number and a host number. The network number is unique, and it identifies a particular network on the Internet while the host number identifies a specific node within that network. The host number is unique within its network.

What is TCP/IP?
TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communications standard for the Internet, and it consists of two layers. The first layer of TCP/IP, the TCP layer, coordinates the breaking down of messages and files into smaller, more manageable segments of data (called packets) that can be sent over the Internet. The corresponding TCP layer on the receiving end of the transmission reassembles the individual packets back into the original readable message.

The IP layer (the second layer of TCP/IP) handles the required addressing information to ensure that each packet reaches the correct destination. Therefore, when a user sends an e-mail, the TCP layer breaks down the message into small packets of data. The IP layer then attaches the correct addressing information to each packet before it is sent. As the individual packets travel to their destination, they pass through many network gateways or routing points on the Internet. These gateways forward the packets along the best path to the destination point. If network congestion is detected, the packets may travel different routes, but they will be reassembled in the correct order by the TCP layer at the receiving end.

What is a DNS server?
The Domain Name Service (DNS) provides a method by which an Internet domain name can be mapped to its corresponding IP address. Because IP addresses are strings of numbers, domain names were created as "handles" that are easier for humans to remember. For example, could be translated into 109.24.872.120, which would be its physical address. A DNS server is simply a computer that runs the DNS service.

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