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Lesson 2 Internet email
Objective Explain how the Internet transfers email.

Internet email

Email is an abbreviation for "electronic mail." An email is an electronic message transferred from one computer user to another. The message can be simple text, or complex documents with images, video, or sound clips.
Like paper mail, email has both destination and return addresses. The syntax for an email address is user@domain, where each domain (such as "redhat.com") can have any number of users.

Email addresses

A user in an email address doesn't have to be a single, real person. A user can be a group of people or a program attached to the address.
Usually, email address domains are Fully-Qualified Domain Names (FQDN) . These domains point to a unique computer on the Internet that is responsible for the user's email. For example, "roger@workstation0.domain.com" is roger's mailbox on the computer work station0.domain.com.
Special information in the Domain Name System (DNS) abbreviates email address domains to just domain names. This information, known as Mail Exchanger (MX) records and describes which host in a network is responsible for handling all that network's email. For example, roger@domain.com could be an abbreviated email for roger@workstation0.domain.com, made possible by MX records

Transferring email

The Simple Mail Transfer Protocol (SMTP), and its updated cousin the Extended Simple Mail Transfer Protocol (ESMTP), transfer email between computers. When you send an email, you connect to your local email handler, supplying the email you want to send. Your local email handler then connects to the recipient's local email handler, and transfers your mail. The recipient's local email handler routes the mail internally, as necessary.
The flow of email between domains.
The flow of email between domains.

This two-server architecture has several advantages. First, your local relay can queue email and automatically reattempt delivery if the remote server is unavailable. Second, the local relay can help prevent local users from trivially forging email, and can help maintain better audit logs.
The next lesson describes email agents.

Internet Email - Quiz

Before you move to the next lesson, click the Quiz link below to check your understanding of email concepts.
Internet Email - Quiz
Simple Mail Transfer Protocol (SMTP): The Internet's fundamental mail transfer protocol.
Fully-Qualified Domain Names (FQDN): A domain name that has all required DNS information: the host, network, and top-level domain.
Mail Exchanger (MX)" "A special host designated to handle all the network's email.
MX records: Records in the DNS that describe which host handles mail for a given domain.

Extended Simple Mail Transfer Protocol (ESMTP): An extension of SMTP, ESMTP is a ubiquitous protocol for email transfer