This report shows the number of permanently undeliverable email addresses. This will be because the email addresses are unreachable, due to being incorrect or no longer in use.
These email addresses are immediately added to your suppression list.
Find out more about different bounce and suppression types.
Using the report
The report will display all the email addresses which have hard bounced.
Clicking on Display will enable you to change the view of this report.
Clicking on Export next to it will provide options to either export the contacts list into a CSV file or create a new address book with them.
To view the drill down detail on other reports, use More reports... (located next to the title of the report). This will provide a menu from which you can select the report type, as shown below.