Hi there,
If you are using site templates to try and use for email campaigns this will not go well.
Is that what you are doing?
If so - stop.
Email systems are not websites so you can not use all the standard code, BC features (accept modules), javascript etc in emails. You need to make custom ones for email campaigns.
If you are not doing the above then an image to the server needs to be of good file size for images, hosted on the site and absolutely linked if coded manually or input via the editor so BC knows to convert the url on campaign publishing.