Can someone tell if you delete their email?
This is what happens when you reply to spam email | James Veitch
Yes they can. If the person that sent you the email is using an email tracking service, which injects a tracking pixel into your email, then they will be able to tell when you opened the email. However they can not track if you deleted the email. ISPs (gmail, hotmail etc) don't 'send' that information back to the ESP.