An invalid certificate error when opening MS Outlook 2010

An invalid exchange server certificate appearing when you start the MS Outlook 20007 or 2010. For example, the web server fully qualified domain name is webmail.whaddya.com.

Background:
Before Office365 hosting our email address (mailboxes), we used webmail.whaddya.com for our Outlook Web Access (OWA) and we bought a SSL certificate to provide secure connection from workstation to server.

I transitioned our email using Office365, so the old Exchange Server and website webmail.whaddya.com is no longer active, so as the SSL expired after a year.

Then, an invalid server certificate now appearing when I started the MS Outlook 2010 application. The MS Outlook still see that webmail.whaddya.com though I am now using Office365 service. Similar to Internet Explorer, the cache records still exist.

To remove the old data e.g. webmail.whaddya.com, follow this guide.
  • Open Regedit
  • Go to HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\AutoDiscover
  • Right click on AutoDiscover, New, DWORD 32-bit value
  • Value name: ExcludeScpLookup
  • Value data: 1
  • Base: Hexadecimal
Click OK to finish.

Close MS Outlook, and re-open again to check if the invalid certificate is gone.

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