Overview of Electronic Mails
Contents
E-mails Overview
Origin of E-mail
Email Operation
Email Operation (Cont.)
Message Format
Message Format – Example
Types of Emails
Uses of Emails
Problems
Case Studies
Webmail Providers and Products
Recap

Email Operation (Cont.)

The MUA formats the message in email format and uses the submission protocol, a profile of the Simple Mail Transfer Protocol (SMTP), to send the message to the local mail submission agent (MSA), in this case smtp.a.org.
The MSA determines the destination address provided in the SMTP protocol (not from the message header), in this case bob@b.org. The part before the @ sign is the local part of the address, often the username of the recipient, and the part after the @ sign is a domain name. The MSA resolves a domain name to determine the fully qualified domain name of the mail server in the Domain Name System (DNS).
The DNS server for the domain b.org (ns.b.org) responds with any MX records listing the mail exchange servers for that domain, in this case mx.b.org, a message transfer agent (MTA) server run by the recipient’s ISP.