Recently our Dynamics CRM Online instance was upgrade to Update 1 which is something we were eagerly awaiting.
The upgrade was relatively seamless, however we noticed immediately afterwards that emails weren’t sending out of CRM. This affected workflow-driven emails as well as manually created emails. As a result all our emails stuck in the “Pending Send” state.
We worked with Microsoft support to diagnose the issue and ultimately found (albeit taking longer than I would have liked) that the upgrade had changed our email process setting to use the “Dynamics CRM Email Router” instead of “Server-Side Synchronization”.
Just something to be wary of for anyone else going through the upgrade process. An explanation hasn’t been given/found as to why it switched back to the Dynamics CRM Email Router which we had used prior to the upgrade to 2015, however upon switching back everything worked instantly.