Page Settings
The page setting issue at reception is due to the original dimensions of the images of your newsletter.
The message editor enables you to resize an image thanks to the “Image properties” by typing in your own length and width.
This resizing isn't taken into account by some email clients like Outlook. The email client displays the real size of the image. You can check the real size by clicking on the circle symbol next to the dimension fields.
If the dimension is not the one you want, click on “Explore the server”. Search for your image and use the right click of the mouse (Ctrl click for Mac) to resize your image.