TLS, or Transport Layer Security is a protocol that is an industry standard designed to protect the privacy of information communicated over the Internet. TLS is used in many web browsers and applications that communicate over HTTPS and TCP. Until now all Dynamics 365 online versions supported TLS 1.0, 1.1 and 1.2, but starting with the upcoming release of the July 2017 update for Dynamics 365 (online), version 9.0, Microsoft will begin blocking connections from clients or browsers that are using TLS 1.0 and 1.1. Versions 8.x and 7.x of Dynamics 365 will not be affected with this change, and will continue to provide support for TLS 1.0, 1.1, and 1.2 as they do today.
All supported browsers for Dynamics 365 (versions 2015 – Version 9.x) currently comply with the TLS 1.2 standards and will continue to work as before. However, if TLS 1.2 protocol is disabled in your browser or if you utilize a custom Windows client built with .NET 4.5.2 you will be affected and lose connectivity to any CRM Online instances with the July 2017 update for Dynamics 365 (online), version 9.0. If you have a non-Windows application that connects to a Microsoft Dynamics 365 Customer Engagement instance you will need to verify that the technology stack you used supports TLS 1.2.
For additional information about the Microsoft TLS 1.2 Support click here.