With the release of Dynamics 365 Customer Engagement (9.0), older versions of TLS (1.0 and 1.1) connections will be blocked and only connections using TLS 1.2 will be supported. If you are connecting a Microsoft Dynamics 365 for Outlook client on version 8.x to a 9.x Dynamics 365 instance, an update will be required for the clients.
If you have been running recently into some strange unexplained connectivity issues to Dynamics 365 CE Online, then the chances are this might be due to TLS incompatibility between Dynamics and your client code.
I am excited to announce the release of the XrmToolBox Plugin for the Online Management API. This allows Dynamics 365 administrators to leverage capabilities of the API not available through any existing user interface.