Hello @SarahMadderom ,
For the advertisers, it's going to depend on whether they're trying to do banners that are much shorter than they are wide, or if they're doing large singular images with multiple brands spread throughout, or doing standalone images for each individual brand. How they want to add the ads will drastically affect the recommendations.
If they're doing a single image with all the brands, then the only thing they need to keep in mind is that we compress images wider than 1200px, meaning they should avoid going larger than that if they want to avoid the possibility of the image becoming blurry. If they're doing individual images for each brand, then the only thing to really keep in mind is how emails rearrange in mobile view, so images larger than 480px will fill the entire width of a mobile device.
If they're doing banners, they need to keep in mind that the default width of emails is 600px, but can be widened up to 1200px. So depending on how tall the banner is as well, you may need to widen your email significantly to accommodate the banner. In mobile, this will likely be the most noticeable if the width is much greater than the height, since the image will be forced down to 480px wide, and its height flattened proportionately.
For simplicity's sake, tell the advertisers that the images should not run any wider than 1200px. If they're doing individual images for each brand, make them particularly small (i.e. icon size - 100x100 max) so the mobile view doesn't become noticeably bloated.
I'd recommend taking a look at these articles for a little more info on optimizing your image sizes, and to make sure you're making adjustments to your email's width as needed for a good desktop view. Make sure to also preview or test send the email in both desktop and mobile formats, prior to sending it out.
Preparing images for upload
Resizing images for optimal desktop and mobile views
Using the section editor for email backgrounds, widths, and borders
... View more
