Hello @user0055171 ,
At this time there isn't anything within the editor that provides the exact sizing of the image as it appears embedded in the email. The true size / resolution of the image when downloaded / saved from the email will be whatever its metadata says it is. You can view the true size of the image, based on its metadata, by viewing it in the Library or in the Image Editor screen.
Click here for an overview of the different ways you can view an image's size.