All images that are sent with Apple Mail shown as poststamp size at the receiver. How do I fix this?

Whenever I sent an Email containing an image the receiver gets the image in poststamp size. Even with pictures from a camera, which are 3200x2400, they still remain displayed at the receiver as some kind of picture of 200x150..

I'm aware of the dropdown to choose from "actual size, small, medium, large", but I've tested with this feature and none of the solves the issue.

I would almost say there is some overriding rule that sets the image at small size.. perhaps a terminal command could resolve this?

Anyone might have a solution ?