You'll want to do this if you read email in Mail and another program (or our Webmail system). With the Apple Mail application, it's possible to leave a copy of each message on the mail server after you read it. If you’re using an older version of Apple Mail, such as the version included with Mac OS X “El Capitan” or “Yosemite”, see Leaving Mail on the Server with Apple Mail in “El Capitan” and Earlier instead.
This page is for the macOS “Sierra”, “High Sierra”, “Mojave”, “Catalina” and “Big Sur” (2016 and later) versions of Apple Mail.
