Pluto Mail

It would seem that they're achieving this by embedding remotely hosted images as the content of the email

@_jacksmith It would be similar with Movable Ink technology https://movableink.com/ (MI are using it for email marketing only)

@jberrebi cool; I didn't know that was the main tech behind MI (I haven't looked into it too much tbh). MI is a lot more advanced than this I imagine; Pluto still looks very much MVP stage.