Images can have a significant impact on your email campaign. They are a great tool to represent the brand's tone of voice and deliver the right message.
While the text will weigh only a few bytes and immediately display, images are generally heavier and can take some time to load. So, you should carefully limit the weight (and the number) of images in your HTML newsletter.
If your images are large-size files, there are two negative consequences.
It will take a while for them to load when your reader opens the email, and they will likely not see any image.
Your email size will increase, which can cause email spam filters to block it (more detail on deliverability here)
Conversely, images with the correct file size for emails will load and display quickly, create a positive user experience, help ensure deliverability, and optimize the conversion you want.
How much weight should your image carry in your email?
We strongly recommend less than 1 MB among all images to allow your contacts to have a manageable latency.
Magnetiq template editor won't allow uploading more than 2 MB for each image.
How to resize and compress images for email marketing
Here are some suggestions that you might want to pass on to your design agency:
Keep your image size no wider than 600px
Use the proper compression: JPEG for photographs / GIF for logos, line art, or images with limited palettes and flat colors
Use as few frames as possible in animated GIFs
If your image has text, consider moving it outside and treating it as HTML: this might help resize the image, remove unnecessary frames, and make the text readable on smartphones