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To monitor SharePoint content that is accessed via external locations, you can use the _referrer parameter whenever you publish a link to SharePoint and you wish to track the source of the referring application or page.
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For example, if you have included an internal link in a promotional email add the referrer parameter to track the users who visited your site via this link. Define a unique referrer value that will be displayed in reports, such as referrer=email_promotion_Dec_2020 in order to display the link accordingly:
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