EMail 101 - Sponsored Whitepaper

The flow of email on the Internet is both surprisingly simple and surprisingly complex. It is simple because the basic email protocols are decades-old plain-text protocols with very simple denitions. It is complex because many tiny details can have a profound inuence on how mail ows and on how to interpret message headers. This document will teach you how email ows on the Internet, and how to interpret message headers to determine the history of a piece of email. These are valuable skills for trou- bleshooting your email setup or even just for guring out how a particular email arrived in your inbox.

A protocol is simply an agreed-upon way for two pieces of software or hardware to commu- nicate. It's the basic set of ground rules to ensure the two ends understand the conversation that's going on between them. Protocols are typically developed in many layers, and a whole layered set of protocols is sometimes called a protocol stack. For example, two computers on a LAN use protocols such as these:

At the lowest level, the Ethernet physical protocol denes the voltage levels and timing on the Ethernet cable.

At a slightly higher level, the Ethernet data link protocol denes the bit patterns that make up a valid Ethernet frame.

At higher levels are network, transport and application protocols, which will be dis- cussed later.