One of our PCs would not connect to Exchange without asking for a password and we tried new profiles, un-ticking specify certificates options, choosing basic authentication.

Eventually we had to make a change to the registry:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\RPC

You may have to create the RPC key if it does not exist

Add a DWORD value called UseWindowsUserCredentials and set its value to 1

Then choose basic authentication under the Exchange HTTPS connection settings in Outlook.

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Sometimes just picking NTLM/password rather than ‘negotiate security’ can solve many issues.

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