As announced in April 2017, important changes are coming for accessing Office 365 services with Office client.
In October 2020 all Office clients which are NOT either Office Pro Plus (aka Office Click to Run) or Office in Mainstream support will blocked when accessing Office 365 services (Exchange, SharePoint, Skype….)
So start your Office client assessment to prepare your migration to Office Pro Plus (best option) or engage your favourite IT partner to help you.