A customer of mine just got hit by this so I figured I would make sure you saw it again as well.
Effective October 13th, 2020, Office 365 will only allow Office client connectivity from subscription clients (Office 365 ProPlus) or Office perpetual clients within mainstream support to connect to Office 365 services. (Please refer to the Microsoft support lifecycle site for Office mainstream support dates.)
|Connectivity to Office 365||Impact of change||Technical implications||Recommended actions|
|Office 365 ProPlus or mainstream Office clients||No change||Plan for regular updates to stay within support window||No action required|
|Office clients outside mainstream support||client connectivity no longer available||Office desktop client applications, such as Outlook, OneDrive for Business and Skype for Business clients will not connect to Office 365 services||Upgrade to current version of ProPlus or mainstream Office clients or use browser or mobile apps|
|browser and mobile apps||No change||No change||No action required|
|Office desktop clients outside mainstream support not using Office 365||No change||Set your own desktop upgrade timeline, in line with your on-premises server upgrades. When planning to move to Office 365 services, an Office client upgrade will be required||No action required|