iOS 15 introduced new privacy features, including one big change called 'Mail Privacy Protection'. When enabled, all images are loaded via Apple's proxy servers to mask the recipient's IP address.
In our testing, this has occasionally caused certain mail images to not load correctly at all (you should see a hint at the top of the Mail app):
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If you are unable to load the images in your email, try deactivating this feature and sending your email again.
To deactivate Mail Privacy Protection, open the Settings app on your iPhone, and choose Mail > Privacy Protection > Protect Mail Activity
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