"This content cannot be displayed in a frame" when you view Outlook Web App in a Page Viewer Web Part
Consider the following scenario:
You add a Page Viewer Web Part to your Microsoft SharePoint Online page.
Within the properties for the Web Part, you configured the Link setting to point to the Microsoft Office 365 Outlook Web App.
In this scenario, when you view the Web Part on a SharePoint Online page, you receive the following error message:
This content cannot be displayed in a frame To help protect the security of information you enter into this website, the publisher of this content does not allow it to be displayed in a frame.
This issue occurs because the Outlook Web App can't be opened in a frame.
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