No Chrome extension can know which images are being used to track email opens. If you want to disable that sort of tracking you should disable images/external resources completely. Otherwise you're just getting a false sense of security.
I speed through email with keystrokes and zero mouse movement, and I can use email with ease on even the slowest of satellite or 2G network access.
Finally - and this is my favorite part - since I use pine, and my engineers at rsync.net also use pine, not one single intra-company email has ever traversed the Internet. Ever.
All intra-company email is simply a local copy operation on a single mail server.
What does the mail client have to do with this? I use Thunderbird with Gmail, and, since all of my contacts use Gmail, not one single email has ever traversed the Internet, ever.
With TLS-enabled mail servers, this isn't very relevant a metric.
They still have the meta-data, the actually interesting stuff.
http://www.nybooks.com/blogs/nyrblog/2014/may/10/we-kill-peo...
Also increasingly, mail clients are sending only html without a text/plain part, and w3m on emacs renders those nicely.