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You can also do this if you want your old incoming mail to be permanently stored in our backup system (see "E-mail backups" on our backup policy page for more details).
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If you don't set up Mail to leave your messages on the server, it will delete the messages as soon as it connects to read mail, and the other program (or Webmail) won't be able to see the messages. 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.
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This page is for the macOS “Sierra”, “High Sierra”, “Mojave”, “Catalina”, “Big Sur”, “Monterey” and “Ventura” (2016 and later) versions of Apple Mail.
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