Microsoft 365 Exchange Service Terms
"We strive to keep the Services up and running; however, all online services suffer occasional disruptions and outages, and Microsoft is not liable for any disruption or loss you may suffer as a result. In the event of an outage, you may not be able to retrieve Your Content or Data that you’ve stored. We recommend that you regularly backup Your Content and Data that you store on the Services or store using Third-Party Apps and Services."
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