If you’ve ever worked in print you know when the publisher says your ad needs to be 8.5×11 you better make it that size or you’re not getting published. Digital media works a bit differently, but there are still recommendations. We recommend a postcard format for email broadcast.
You might be asking why. The answer is the ensure that your message remains above the “fold”, and everything is visible without scrolling. So please, stop sending us print ads and start thinking about the medium you’re marketing in.