Microsoft was experiencing a global DNS issue that is preventing Office 365 users from authenticating. This appears to have affected some DOI VPN users. Microsoft seems to have been able to correct the issue. However, some users are still reporting that they are still having activation problems.
Logging out and back in to Office 365 of an Office application fixes the issue in many cases. If the issues still persists, Microsoft has an Office 365 Troubleshooter that has fixed several users authentication issues. It can be found here:
Support and Recovery Assistant for Office 365
