never rely on someone else's stats for your own site.
are you allowed cgi-bin on the server?
there are small perl scripts that query the visiting browser of browser type, IP address, operating system, last link, directed link, and email (if configured on the browser), and other things.
just match IP address or email addy with the list of those who were sent an email.
my funny story (back in the day-early'90s, animated gifs were just the rage):
I created a website with meta tags on the front page. Some of the keywords were "Thomas" (my real name), "Heather" (my girlfriend at the time), "pics" (we had photos of the town and some vacation pics uploaded).
I had a script that queried visiting browsers of just about everything. A few hits came from people using yahoo or altavista (the "google" of the 20th century) searching for "Heather Thomas pics." Some of these queries came from big corporations during work hours. At the time, web surfing for pics were absolutely forbidden for most big companies.
I should have emailed one of the searchers for be so naughty. I wonder if that would make them paranoid to know that someone knows of their surfing habits?
😛