How does a case manager recieve bell and email notofication when a email message is responded?

Summary:

We are trying to set up notifications to the assigned Case Manager when a case conversation is responded via E-mail, but no notification is getting triggered as per my groovy script. However, I have noticed that by default, there is a bell notification which triggers when email/web message is recieved by the case manager. I am not sure how that notification is triggered. I am looking to set up similar notification on email as well.

Below is the screenshot of Bell notofication:

I tried below groovy script under Case Message> server scripts -

if(MessageTypeCd == 'ORA_SVC_CUSTOMER_ENTRY'||MessageTypeCd == 'ORA_SVC_RESPONSE' ){