Make sure your images are sized correctly to avoid squishing or stretching. In the image editor we provide you with a recommended size. Image files should be formatted as JPG or PNG to ensure they’ll display correctly across various email programs.
My Email Gets Clipped
Try to keep the size of your email template file somewhere around 110 kb. Every decent template will fit in this size. But if you decide to create a huge email you may want to keep in mind that Gmail will display the first 110 kb of your email and clip off the rest. To see the rest you will need to click on a button.
What About Images?
The 110kb will only count code, so don’t worry about the images. Image optimization is however just as important, because you don’t want your clients to stand in front of the PC for 50 seconds waiting for a 2MB image to get loaded, so make sure you optimize your images the best you can.
I get Spam Warnings
It’s being said that badly written code might cause spam warnings, however this is not really entirely true. It’s true that very badly written code might end up causing all sorts of problems, however the most usual problem when spam filters react comes from badly written content, and the overuse of certain keywords.
Some spam filters will flag emails based on specific content or images they contain, but there’s not an all-encompassing set of best practices to follow or things you absolutely need to avoid.
We recommend reading this great post from Mailchimp for further info on this matter: How to avoid spam filters.