BizTalk 2013R2 SB-Messaging: The X.509 certificate CN=servicebus.windows.net is not in the trusted people store.

The Problem: After configuring a brand new BizTalk 2013R2 production environment and requesting the needed firewall exclusions to the security department, we were unable to send messages to Azure ServiceBus using the SB-Messaging adapter in BizTalk 2013R2 (using ACS authentication). We found the following warning in the EventLog: The adapter “SB-Messaging” raised an error message. […]