SMTP and MIME

Finally, we'll round out our exploration of the application-layer protocols with what is probably the second most common protocol (behind HTTP). And yet, as commonplace as it is, I would guess that a staggering number of people who benefit from SMTP don't even know it exists. So, what is it? How would we use it, and why would we use it?

The email protocol

First defined all the way back in 1982, the Simple Mail Transfer Protocol (SMTP) is the de-facto protocol for transmitting electronic messages. It's a connection-oriented protocol using the client-server architecture we've become so familiar with over the course of this book. Similar to FTP, SMTP transactions happen over a sequence of commands...