"There is one more difference between you and the average user that’s even more damaging to your ability to predict what will be a good user interface: skills in using computers, the Internet, and technology in general. Anybody who’s on a web-design team or other user experience project is a veritable supergeek compared with the average population. This not just true for the developers. Even the less-technical team members are only “less-technical” in comparison with the engineers. They still have much stronger technical skills than most normal people."
paper w stats
http://www.oecd-ilibrary.org/education/skills-matter_9789264258051-en
So I have a stupid question. How do I find out what percentage of the emails sent by John Smith last month were about sustainability? Is there any convenient way I don't know about?
Assuming they means "percentage of emails sent by John Smith to you" and assuming you have a reasonable email client, it's should work like this: