Some of the default settings will delete the mail from your mailbox once it is downloaded, which may not be what you plan to do. Both Gmail's POP settings and the POP settings in most mail clients offer the choice of what to do with the email messages once they are downloaded by the client.When you would like to backup your messages, you will open the client and wait for it to download your mail.
(Below, we provide instructions for backing up your mail with Thunderbird, which is available for Mac, PC, and Linux.) You are going to set up the email client to download your emails using POP, which is a mail protocol - a way of downloading your mail.
To back up email locally, you will need to configure an email client to download your mail. We don't recommend following these instructions unless you have a compelling reason. While most of us will NOT need to store mail locally, some may have a reason: for example, staff who are planning to leave the University and would like to leave a copy of their emails with a department. Google backs up data for the services it offers. Since Gmail stores your mail in the "cloud", it is not downloaded to your computer (stored locally).