1. Launch the Exchange Admin Center
Click on the start button and then expand Microsoft Exchange Server 2016 and click on Exchange Admin Center.
2. Enter your login details
Enter your login details on the webpage and press enter.
3. Navigate to servers
Click Servers on the left and then servers on the top.
4. Editing server options
Click on a server and then either double click the server name or click the pencil button to edit the properties.
5. Outlook Anywhere
On the new screen, click Outlook Anywhere at the bottom of the list.
6. URL configuration & authentication.
Enter in the external/internal URL and select your authentication method.
7. Save your settings.
Click the Save button to save the settings you configured.