When Dynamics 365 web servers are configured behind a load balancer, exceptions may occur from WCF-based clients such as the Outlook Client, Email Router, or SDK applications when communicating over web services. Examples of these exceptions may include:
"An unsecured or incorrectly secured fault was received from the other party"
The issue occurs due to missing or incorrectly configured persistence settings on the load balancer, which can cause WCF failures when the web server attempts to read a token that was issued by a different web server.
Dynamics 365 requires IP based persistence to be configured on the load balancer.