To Enable/Disable Autocomplete in Outlook, try the following:

1. Open Outlook, click Tools – Options

2. Click “Email Options” button then “Advanced Email Options”

3. Check/Uncheck “Suggest names while completing To, Cc, Bcc fields” to enable/disable Autocomplete.

4. Click OK,OK, Apply & OK.

This should enable or disable AutoComplete in Outlooka s you need.

If you are an organisation and want to enable/disable Autocomplete on all your network domain computers then you can use Group Policy to disable from Windows Registry

Look for the key “ShowAutoSug” key under

[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Preferences\]

and set its value as follows

“0? – Disable Autocomplete
“1? – Enable Autocomplete

NOTE: Depending on Office version the registry path may vary for instance as "10" or "11"