Which Office version are supported with Office 365 ?
Many web pages, including Microsoft support pages, tell us that support for Office 2016 with Office 365 ends on October 13, 2020. These same sites also indicate that it will simply be impossible to connect to Office 365 services with an Office 2013 version… all of this information dates from 2017 and Microsoft has since backed down.
Indeed Microsoft has changed its position by pushing the support of Office 2016 with Office 365 until 2023:
Office 2016 connectivity support for Office 365 services
In addition, we are modifying the Office 365 services system requirements related to service connectivity. In February, we announced that starting October 13, 2020, customers will need Office 365 ProPlus or Office 2019 clients in mainstream support to connect to Office 365 services. To give you more time to transition fully to the cloud, we are now modifying that policy and will continue to support Office 2016 connections with the Office 365 services through October 2023″https://www.microsoft.com/en-us/microsoft-365/blog/2018/09/06/helping-customers-shift-to-a-modern-desktop/
In addition, the Microsoft support site clearly states that connections from older versions (2013 for example) will not be blocked:
Microsoft won’t deliberately prevent you from connecting to the service, but the quality of your Office 365 experience may diminish over time.https://products.office.com/en/office-system-requirements#coreui-contentrichblock-nnuz9v1
A lot of information is available in this Office 365 e-book, included this problem.