So Outlook was crashing for a users PC (Windows 10/Outlook 2013). The cause of the crash was a buggy Add-In. Outlook wouldn’t then login, the username/password dialog kept prompting.
So after checking
autodiscover doing IPCONFIG /flushdns Cached Credentials Hacking the registry
Nothing working… We checked IE and there was a proxy, once the proxy was removed everything starting working, including Windows Update and Microsoft Offline files!