Symptoms
When replying to a SmartAction email, the action is not taken, and there is no response from K2
In the HostServer logs the following error is logged:
The request failed schema validation: The element 'ItemShape' in namespace 'http://schemas.microsoft.com/exchange/services/2006/messages' has invalid child element 'Header' in namespace 'http://schemas.xmlsoap.org/soap/envelope/'. List of possible elements expected: 'IncludeMimeContent, BodyType, AdditionalProperties' in namespace 'http://schemas.microsoft.com/exchange/services/2006/types'.
Diagnoses
This has been seen before when trying to use Exchange 2013 EWS to connect to an Exchange 2010 mailbox.
Resolution
Delete and recreate the mailbox in Exchange 2013