That should be the default behavior, not a special lock down option that also disables other features.
Why can't they just make it like most email clients? No preview by default, give a banner with an option to explicitly allow a preview for that specific message or conversation?
No such thing as completely idiot proof. But I think we can all agree an exploit that requires a click is a lot better for the intended victim than one that doesn't. This way they at least have a chance to not click it. Then we can start tackling the other problems with separate solutions
Why can't they just make it like most email clients? No preview by default, give a banner with an option to explicitly allow a preview for that specific message or conversation?