The response email will be sent out if you set an email header charset of a Notification Method to UTF-8 as shown below.
1. Log into Service Desk and open 'Administration' tab.
2. Go to 'Notifications' > 'Notification Methods' and open "Email".
3. Click on <Edit> and change Notification Method as shown below.
pdm_mail -H UTF-8
4. Click on <Save> button to save the change.
You can create a new Notification Method on the above step 2 instead of changing an out-of-the-box method, and specify it to in the 'Reply' drop down list.