Office 365 Wave 15 stopped an Outlook 2007 client connecting

….but that isn’t the whole story.

There must have been a problem with this XP Machine for a while, but the Wave 15 upgrade made it stand out.   

The problems seemed to stem from a missing certificate which meant that the outlook.com chain was broken.  I was getting “The Issuer of this certificate could not be found” on the outlook.com cert both in Outlook and Webmail / IE.   In the chain, I found MSIT Machine Auth CA 2 and Microsoft Internet Authority mentioned.  

The fix itself was simple in the end, but it did take a lot of searching.   Which is why I am putting this here for others.

Download the latest Root Certificate and install in the Trusted Root Certificate Store on your machine.

Link to cert

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