Yep, we're on the same page. The wording they use is "In some cases, senders may be able to know whether an individual has opened a message with unique image li

Yep, we're on the same page. The wording they use is "In some cases, senders may be able to know whether an individual has opened a message with unique image links." but I'd expect the tracking URLs themselves to be unique (most are, they are tied to an email so they know who opened the email and who didn't) so they would most likely bypass this cache. I expect the "some cases" refers to the ones where it simply gives you a count of people who opened your email, and does it by simply having a generic tracking URL.