The size and position of emails from Online Express are predetermined based on industry best practices. The e-mail marketing format uses table based layouts and limited CSS styling in order to work properly in various email clients.
Formatting the style and layout of your e-mail:
Best fit vs. actual size images: Either option should work fine on mobile devices - if you specify a width of 525 pixels, it will be that size on desktop clients, but scale down for mobile. In general, "Best fit" does this with even less effort on your part, the image simply fills the space that it can. We see "best fit" used the majority of the time.

Column stacking: Columns stack from left to right, just as you would expect. Keep this in mind when you design your content. Left columns stay on top, right columns wrap underneath.

We recommend using the test email feature to get an idea of how the desktop versus mobile device will display.

Check out the Blackbaud Online Express Community to see how other users work with email responsiveness: