Steps to start/stop Workflow Notification Mailer (fnd_svc_component)

1. Check workflow mailer service current status

SELECT running_processes

FROM fnd_concurrent_queues

WHERE concurrent_queue_name ='WFMLRSVC';

Note : Number of running processes > 0 

2. Find current mailer status

SELECT component_status

  FROM fnd_svc_components

 WHERE component_id =(SELECT component_id

                        FROM fnd_svc_components

                       WHERE component_name ='Workflow Notification Mailer');

Possible statuses are :
    RUNNING 
   STARTING 
   STOPPED_ERROR 
   DEACTIVATED_USER 
   DEACTIVATED_SYSTEM 

3. Stop notification mailer 

DECLARE

   p_retcode    NUMBER;

   p_errbuf     VARCHAR2(100);

   m_mailerid   fnd_svc_components.component_id%TYPE;

BEGIN

SELECT component_id

INTO m_mailerid

FROM fnd_svc_components

WHERE component_name ='Workflow Notification Mailer';

   fnd_svc_component.stop_component (m_mailerid,

                                     p_retcode,

                                     p_errbuf

                                    );

COMMIT;

END;

/

4. Start notification mailer 
DECLARE

   p_retcode    NUMBER;

   p_errbuf     VARCHAR2(100);

   m_mailerid   fnd_svc_components.component_id%TYPE;

BEGIN

SELECT component_id

INTO m_mailerid

FROM fnd_svc_components

WHERE component_name ='Workflow Notification Mailer';

   fnd_svc_component.start_component (m_mailerid,

                                      p_retcode,

                                      p_errbuf

                                     );

COMMIT;

END;

/