Email is the most-widely used Internet service. The first email message was sent in 1971. Since then, email has become an extremely popular communication tool. Millions of people have mailboxes (disk spaces) allocated in which they received messages sent to them across the Internet. To receive emails, a person must have an email address. The email address of a person is composed of two parts: The name identifying his/her mailbox and the domain name of the computer at which this mailbox is allocated.

The servers that provide the email service to the users are called email servers. The Internet has tens of thousands of email servers running. An email server is actually composed of two servers. The first is the SMTP server where SMTP stands for the Simple Mail Transfer Protocol which is the protocol that defines the rules for handling your outgoing mail (the mail you send). The SMTP server is responsible for reaching the computer that has the mailbox of your email recipient. Once reached, the SMTP server delivers your email to the SMTP server running on that computer. That SMTP server then delivers the received email to the second component of an email server. This is the POP3 server, where POP3 stands for the Post Office Protocol version 3 which is the protocol that defines the rules for handling your incoming mail (the mail you receive). The POP3 server running on the recipient’s machine stores the received email in the recipient mailbox and it waits to be accessed by the recipient’s email client.

People send and receive emails through email clients that are stand-alone as Microsoft Outlook or Outlook Express or that are web-based as those offered by SOL and Yahoo!. Email clients today allow you to attach files to your text email messages. These attachments may contain text, audio, image, or video data.