Offtopic question: How can you (reliably) meassure open rate of a newsletter? I'd assume mail clients as well as webmailers preventing any sorts of tracking, and tracking only those that have lax privacy requirements would taint the whole metric, wouldn't it?
How we calculate open and click rates
The open rate is a percentage that tells you how many successfully delivered
campaigns were opened by subscribers. To find this out, Mailchimp loads a
tiny, transparent image into each campaign, and counts how often the image is
loaded among the delivered campaigns. The image is invisible to your
subscribers.
