Send Dunning Letters - incorrect email address

Summary:

What happens to dunning letters that are automatically fired for customers who have a bad or incorrect email address entered within Contacts?

Content (please ensure you mask any confidential information):

For example, if you send an email in Outlook and the email address is bad or incorrect then you receive an Undeliverable Response from the Mail Delivery System, however when Dunning Letters are created for the customer and the customer has a bad or incorrect email address setup within Contacts then when the dunning letter ESS jobs complete successfully and the strategy task completes normally there is no 'call back' to Oracle to highlight that the dunning letter were not delivered due to the bad email address. How does the customer keep track of Dunning letters that were