Microsoft announced that they will move away from Basic Authentication access for EWS, with support ending Oct 13, 2020. You can read more about this announcement on their TechNet page
What does this mean for OnBoard customers using the OnBoard for Exchange Integration with Office 365?
Development plans are under way to migrate our Exchange integration solution to use Microsoft Graph and OAuth 2.0. This development will begin later in 2019, with plans to finish by early 2020, ahead of the October 2020 sunset date.