We recommend a maximum size of 100 - 150kb per image. If there is only one large image in your campaign, a larger image size of up to 600kb is acceptable.
Any image content larger than those guidelines can cause delays and issues for recipients trying to view your campaign.
Images can be resized after they have been uploaded by clicking the down arrow next to the image name and selecting "Edit."
Larger files (e.g. PDF) can be uploaded because their file size is not actually calculated as a part of the content in your campaign - they are stored on our servers and only represented by links within your campaign. This means it is possible to upload files of 5MB and larger. However we do suggest using smaller file sizes, as it will take a significant amount of time for recipients to download that size file after clicking the link in your campaign.