After your e-mail client knows your e-mail address, it's going to need to know where to look for
incoming e-mail and where to send outgoing e-mail.
Your incoming e-mails are going to be on a computer called a POP server. The POP server –
usually named something like pop.smallnetwork.net or mail.smallnetwork.net – has a file on it
that is associated with your e-mail address and which contains e-mails that have been sent to
you from someone else. POP stands for post office protocol.
Your outgoing e-mails will be sent to a computer called a SMTP server. This server – named
smtp.smallnetwork.net – will look at the domain name contained in the e-mail address of any
e-mails that you send, then will perform a DNS lookup to determine which POP3 server it
should send the e-mail to. SMTP stands for simple mail transfer protocol.
When you start up your e-mail client, a number of things happen:
1. the client opens up a network connection to the POP server
2. the client sends your secret password to the POP server
3. the POP server sends your incoming e-mail to your local computer
4. the client sends your outgoing e-mail to the SMTP server.
The first thing to note is that you do not send a password to the SMTP server. SMTP is an old
protocol, designed in the early days of e-mail, at a time when almost everyone on the
Internet knew each other personally. The protocol was written with the assumption that everyone who would be using it would be trustworthy, so SMTP doesn't check to ensure that
you are you. Most SMTP servers use other methods to authenticate users, but – in theory –
anyone can use any SMTP server to send e-mail. (For more information on this, see section
9.2.4 Forged Headers.)
The second thing to note is that, when you send your secret password to the POP server, you
send it in a plain-text format. It may be hidden by little asterisks on your computer screen, but
it is transmitted through the network in an easily readable format. Anyone who is monitoring
traffic on the network – using a packet sniffer, for instance – will be able to clearly see your
password. You may feel certain that your network is safe, but you have little control over what
might be happening on any other network through which your data may pass.
The third, and possibly most important thing that you need to know about your e-mails, is that
they are – just like your password – transmitted and stored in a plain-text format. It is possible
that they may be monitored any time they are transferred from the server to your computer.
This all adds up to one truth: e-mail is not a secure method of transferring information. Sure, it's
great for relaying jokes, and sending out spunkball warnings, but, if you're not comfortable
yelling something out through the window to your neighbor, then maybe you should think
twice about putting it in an e-mail.
Does that sound paranoid? Well, yeah, it is paranoid, but that doesn't necessarily make it
untrue. Much of our e-mail communications are about insignificant details. No one but you,
Bob and Alice, care about your dinner plans for next Tuesday. And, even if Carol desperately
wants to know where you and Bob and Alice are eating next Tuesday, the odds are slim that
she has a packet sniffer running on any of the networks your e-mail might pass through. But, if
a company is known to use e-mail to arrange for credit card transactions, it is not unlikely to
assume that someone has, or is trying to, set up a method to sniff those credit card numbers
out of the network traffic.
