In order for images and in turn the entire email to display well across various email platforms - including mobile devices - each image in email messages needs to be resized to fit the container they are added to.
How to resize images
STEP 1) Right-click the image in the image browser and select the "Resize" option:
STEP 2) Enter the width to resize the image to (height is automatically calculated).
Optional: Turn off the "create new image" checkbox if you want to overwrite your original image, otherwise a new image file is created with the new dimensions.
STEP 3) Double click the new/resized image in the image library to add it to your message.
Tip: create folders in the sidebar of the image library to help oragnize/find images.
What are the image dimensions to use in email messages?
Image sizes vary in different sections of emails. Refer to the illustration below for required widths: