More and more e-mails, and therefore also newsletters, are being read on mobile devices. And on mobile devices, the so-called pixel density continues to increase. Some time ago, double pixel density was the measure of all things, but today many devices are already in use with four times the pixel density. Some notebooks and desktop PCs also have higher pixel densities.
What does this mean for your newsletters?
You should optimise them for high-resolution displays. Unfortunately, it is not so easy to use the "srcset" attribute, which is widely used in web design. It can be used, but many mail clients ignore it. So if you still value good image quality, it makes sense to double the resolution for the start. In our experience, this is a common and very pragmatic approach. The file size is about four times as large as the original image - because the image is twice as wide and twice as high. Then you have to include the corresponding "height" and "width" attributes. You can then zoom into an image without it becoming pixelated.