The issue appeared to be resolved at 3:15pm PST, consistent with Microsoft's status page: https://status.office.com/.
Posted Mar 15, 2021 - 17:10 PDT
Monitoring
Microsoft just posted a status update: > Current status: We are currently rolling out a mitigation worldwide. Customers should begin seeing recovery at this time, and we anticipate full remediation within 60 minutes.
Posted Mar 15, 2021 - 14:25 PDT
Identified
At approximately 1pm PST, users started reporting errors when attempting to send emails through their connected Microsoft Exchange / Office 365 accounts.