Message SAP XS094 - Action cannot be executed because ESMTP plug-in XString empty

Diagnosis The required method is not executable because the data structure forcommunication between the SAP System and the ESMTP plug-in - theXString - is empty. System Response No action is executed. Procedure The ESMTP plug-in XString has to be filled first by suitable actions.If you, as an end user, receive this message, report this to yoursystem administrator.