Workflow Notifications Not Being Sent

Cause 1:
Workflow Notification Mailer
WF_NOTIFICATION_OUT is the queue where outbound notifications are queued up and WF_NOTIFICATION_IN is where inbound notifications are queued. Workflow Notification Mailer and the following listeners must be running smoothly to keep processing inbound and outbound notifications and flush these two queues. Otherwise, we see huge amount of data getting into one or both of queues leading to diskspace and performance issues. The following listeners must be running:
Workflow Deferred Agent Listener
Workflow Deferred Notification Agent Listener
Workflow Error Agent Listener
Workflow Inbound Notifications Agent Listener

All the Deferred Agent Listeners are Stopped.

As SYSADMIN:Navigate to Workflow Administrator Web Applications > Oracle Applications Manager > WorkflowManager > you notice that "Agent Listeners" are Unavailable.

Solution
As SYSADMIN:Navigate to Workflow Administrator Web Applications > Oracle Applications Manager > WorkflowManager > "Service Components".
Start "Workflow Deferred Agent Listener" , "Workflow Deferred Notification Agent Listener" ,"Workflow Error Agent Listener" , "Workflow Inbound Notifications Agent Listener" , "Workflow JavaDeferred Agent Listener" , "Workflow Java Error Agent Listener".After that, all the notifications should generate correctly.

Cause 2:
Some products may create a user or role without an e-mail, then updates with the e-mail later which would cause those roles to be QUERY where MAILHTML would be expected.

Solution
Check the notification preferences


select *
from fnd.WF_LOCAL_ROLES
where email_address is not null
and orig_system = 'PER'