Are you confusing webmail services like gmail.com with Thunderbird, a local client? They are quite different in their security risks. Loading images by default is very, very dangerous. It could be a virus vector, as there have been security failures in image rendering routines and that has allowed viruses to be installed just be looking at a specially crafted image. More commonly, the images in mail, including spam, are fetched using URLs that tell them that you, specifically you, are reading it, so the know that your email address is good (resellable to other spammers as validated). In any case it's bad for your privacy. So you really should not want to load images without first deciding it's mail you deem safe. What a web mail program can do is load the image itself and try to figure out if it has tracking included and just display a cleaned-up image at you. But a client can't do that by itself as it's already on your home system.