https://userapps.support.sap.com/sap/support/knowledge/en/1831589
1831589 - Complete ERMS WF without delivering E-mail to CRM Agent Inbox | SAP Knowledge Base Article
You need that an Incoming E-mail handled by ERMS Workflow (WS00200001) would NOT be delivered to CRM Agent Inbox, but you need to be able to do further...