Benjamin Mako Hill:
A few years ago, I was surprised to find out that my friend Peter Eckersley — a very privacy conscious person who is Technology Projects Director at the EFF — used Gmail. I asked him why he would willingly give Google copies of all his email. Peter pointed out that if all of your friends use Gmail, Google has your email anyway. Any time I email somebody who uses Gmail — and anytime they email me — Google has that email.
Since our conversation, I have often wondered just how much of my email Google really has. This weekend, I wrote a small program to go through all the email I have kept in my personal inbox since April 2004 (when Gmail was started) to find out.
One challenge with answering the question is that many people, like Peter, use Gmail to read, compose, and send email but they configure Gmail to send email from a non-gmail.com “From” address. To catch these, my program looks through each message’s headers that record which computers handled the message on its way to my server and to pick out messages that have traveled through google.com, gmail.com, or googlemail.com. Although I usually filter them, my personal mailbox contains emails sent through a number of mailing lists. Since these mailing lists often “hide” the true provenance of a message, I exclude all messages that are marked as coming from lists using the (usually invisible) “Precedence” header.