Hi,
Do you mean you want transactions get created even the sender's email is not assigned to any BPs in CRM?
In SPRO->CRM->Basic Functions->Rule Modeler->Define Services, display the service AH_CREATE_SR, we can find that assigned service class is CL_CRM_ERMS_AH_CREATE_SREQ.
In T-code SE24, display method CL_CRM_ERMS_AH_CREATE_SREQ->IF_CRM_ERMS_SERVICE~EXECUTE, there are statements:
bp_number
= service_manager->get_bp_number( ).
IF bp_number IS INITIAL.
lv_error_text = 'No business partner found; transaction was not created'(002).
RAISE EXCEPTION TYPE cx_crm_erms_service_failed EXPORTING shorttext = lv_error_text.
ENDIF.
Maybe you have to create your own ERMS service and your own service class to fulfil your requirement. In standard, many information needed when creating a transaction will be retrieved from the BP which is assigned to the sender's email address. Now you must take care of these information in your ways now since email address is not assigned to any BP.
Best Regards, Corrine