Apple users who are running iOS 15, iPadOS 15, MacOS Monterey or WatchOS 8 (or later) can enable Mail Privacy Protection by opting in within the settings of their device. On iPhone, for example, go to Settings > Mail > Privacy Protection and turn on the Protect Mail Activity option. After upgrading to one of these newest operating systems and opening the Mail app for the first time, it should also automatically prompt users to turn this feature on.