Dear Liz Lister,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Based on your description, I understand that you have a query "Disabling Email Auto-Complete". Before we proceed the investigation, we need more detailed information about the situation you are experiencing.
Please help us in isolating the issue by providing the following information:
- Do you mean that registry keys do not work or that you are unable to apply this registry key to all users?
- How did they apply the changes in registry? Have they opened the Registry Editor > go to Computer\HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\Preferences > add the following items?
- Value Name: ShowAutoSug
- The value of the type: REG_DWORD
- Value: 0

We look forward to hearing from you, please let me know and provide a more detailed description so we can provide you with more specific assistance. Thank you for your cooperation.
Sincerely,
De Paul | Microsoft Community Moderator