Campaign Monitor Email Design Guidelines (scroll down for their discussion on images)
http://www.campaignmonitor.com/resources/will-it-work/guidel...
Image Blocking:
http://www.campaignmonitor.com/resources/will-it-work/image-...
CSS Support:
And people managing these kind of newsletters probably know that. They design nice layouts for their newsletters, with images and fancy stuff to be "visually friendly". And they know people will want to let pictures in, and they know they will then have the possibility to track views. They even include the infamous if this email isn't properly displayed, see it here [http: //link/mail/online/?here_is_who_clicked_this_link=your_name] (usually more subtle than that.)
This complexity is going to make analysis nearly impossible in the future as political (and marketing) messaging becomes incredibly personalized.
(I'm actually author and OP here is my also-HN reading brother who beat me to the punch)
I'm absolutely no mailing specialist, but here is my take :
Your study is quite interesting, but has it any value without you saying which mails your read when ?
Tracking if an email has been read or not is quite simple, providing the email is sent as HTML and the one who reads it is no privacy-nerd (noscript, ghostery, other ways to block external ressources, highly secure mailbox softwares, etc). What if you regularly "read" Obama's mails and not Romney's ones ?
If I were to manage this kind of mailing campain, I'd probably put on hold for a while email addresses who haven't read the last X mails. On the contrary, I would go on sending mails to people reading them. Etc.
Please tell us what you did "read" and when, and what you did not.