"You may have already signed in to Outlook Web App" error when you try to open Outlook Web App in Office 365
- Closing your browser window and signing in again.
- Deleting cookies from your browser and signing in again.
- You try to open an Office 365 Outlook Web App session and an Outlook.com-based Outlook Web App session at the same time.
- The Office 365 Outlook Web App session and the Outlook.com-based Outlook Web App session share the same Outlook Web App server endpoint.
- Set up CNAME records in the external Domain Name System (DNS) server, and set up custom Outlook Web App URLs. For more information about how to do this, see page 19 of the following document:
- Access the second instance of Outlook Web App by using an InPrivate Browsing session in the browser. For more information about InPrivate Browsing, go to the following Microsoft website:
Article ID: 2798988 - Last Review: 07/09/2014 08:19:00 - Revision: 10.0
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