Making sure that your Office 365 services are up and running is not an easy task. As outages to Office 365 are most likely not global, but specifically impacting some users, you need to check your services.
This can easily be done by checking your tenants service status using the API provided by Microsoft. Using this script you can monitor your tenants service status from PRTG.
You will need to do some preparational steps so that the Microsoft API can be accessed, but those are descibed in detail in the blog post linked below.
By the way: An english version is about to arrive soon, with updated pictures and description.
Find the detailed description on https://www.team-debold.de/2016/07/22/prtg-office-365-status-ueberwachen