Just sent out a test email from the newsletter campaign section in 4.20 where you edit and add images to the email that you are going to send out to your customers but when I receive the test email either on the phone or tablet the images are not displayed.
Did you change the URL of the image ? When images are inserted by the editor it just uses the relative address src="/images/uploaded/image.jpeg" So you still see them in the editor But when it is sent and received in an email the address cannot be resolved externally So after you insert the images you need to change the address to be the full address http://yourwebsite.com/images/uploaded/image.jpeg