I had a terrible, deep-history bug cause problems with one of my Office 365-using clients about six months ago. It was a genuine PITA to troubleshoot. Once we

I had a terrible, deep-history bug cause problems with one of my Office 365-using clients about six months ago. It was a genuine PITA to troubleshoot. Once we figured out the source of the problem, I was on the phone with someone from Microsoft who knew exactly what I was talking about, and the available workarounds, within the hour. My clients continue to use Office 365.