TITSUP: Total Inability To Stand Up Products

Loads of people reported that, at around 1245 PT, access to the service went out. Microsoft confirmed shortly after it was having problems, and said it was looking into the matter. Subscribers in New York, Denver, Texas, and Portland, in the US, were, for example, unable to access the service.

We are investigating a problem affecting access to Office 365, and we will post an update as soon as we have more info.
— Office 365 Status (@Office365Status) May 10, 2017

Monitoring site Downdetector was crammed with reports of outages from both coasts of the US and major cities as users reported the cloud-connected Office service to be inaccessible.
we notice they tweeted that as of 1338 PT, sign-in issues are being resolved

Source: Well this is awkward. As Microsoft was bragging about Office at Build, Office 365 went down

The problem with the Cloud