> "Know exactly when and where your email was opened, and see how long your content was viewed."
Since most email applications (including web apps) don't auto-load external images, how exactly is this supposed to be achieved?
Great question. The accuracy definitely isn't 100%, but it's still pretty good. Gmail now loads images by default, as do most desktop (and mobile) email clients. There are a few exceptions, but overall it's not as bad as it appears.
Agreed - Most mail clients do upload on auto.
IIRC, Gmail actually serves cached versions of embedded images using their own domains, which basically means that tracking pixels will get exactly one impression/hit (probably even regardless of the email actually having been opened or not).