How does read-tracking work (a feature I don't even want) with a client-only email solution like this?
When you send the email it generates a unique hash it places a tracking pixel (1x1 transparent gif image) served off a canary mail server into the email with that hash. For a period your client queries them for the a yes/no on if that tracking pixel with the hash has been downloaded.
That is typically how email marketing platforms do it, and it appears to be consistent with the FAQ.