If you have an iPhone, in the settings for the Mail app, there is a "Privacy Protection" section, and inside that it has a "Protect Mail Activity" option. This does not work as advertised and actively worsens your privacy. I told Apple about this early 2025. They discarded the bug, said it works as expected and closed the case.
Apple's "Protect Mail Activity" Doesn't Work - grepular.com
https://www.grepular.com/Apples_Protect_Mail_Activity_Doesnt_Work
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Apple's "Protect Mail Activity" Doesn't Work - grepular.com
https://www.grepular.com/Apples_Protect_Mail_Activity_Doesnt_Work