My messages still don't load remote images and are topped with "Some content in this message has been blocked because the sender isn't in your Safe senders list" followed by a link to add the sender's address to the trusted list and another link to show blocked content in this particular message.
I have Apple's Mail desktop and mobile apps set to not load remote content but I think the default is for them to load.
I wager Outlook users are less likely to have remote images enabled
Some of the biggest companies in Europe use Outlook the desktop client, with said external resources disabled.
May differ in technically more advanced countries, of course.
A desktop client with a thin wrapper around the websinterface would be best.