When I checked last, there are some popular email apps that don't provide an option to disable automatic attachment downloading - like Dropbox's Mailbox and Google's Inbox.
Doesn't google pre-download all images before hand and serve the user a cached copy?
Google apparently still leaks the initial opened and time data.
For those who care, the Gmail app still has the option to not load images. It's why I still use it over Dropbox Mailbox, Google Inbox, and Microsoft Outlook (Acompli).