When you try to connect to an Exchange server in Outlook 2016, you receive one or more of the following error messages:
Information you exchange with this site cannot be viewed or changed by others. However, there is a problem with the site's security certificate.
The security certificate was issued by a company you have not chosen to trust. View the certificate to determine whether you want to trust the certifying authority.
The name on the security certificate is invalid or does not match the name of the site.
The security certificate has expired or is not yet valid.
To prevent this prompt and just fail the connection, install April 5, 2016, update for Outlook 2016 (KB3114972), and then follow these steps.
Important
Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.
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Exit all Microsoft Office applications.
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Start Registry Editor:
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In Windows 10, go to Start, enter regedit in the Search box, and then select regedit.exe in the search results.
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In Windows 8 or Windows 8.1, move your mouse to the upper-right corner, select Search, enter regedit in the search text box, and then select regedit.exe in the search results.
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In Windows 7 or Windows Vista, select Start, enter regedit in the Start Search box, and then select regedit.exe in the search results.
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Locate and then select the following registry subkey:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\HTTP
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On the Edit menu, point to New, and then select DWORD Value.
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Enter FailAllCertificateErrors, and then press Enter.
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In the Details pane, press and hold (or right-click) FailAllCertificateErrors, and then select Modify.
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In the Value data box, enter 1, and then select OK.
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Exit Registry Editor.
