This report shows the number of undeliverable email addresses due to soft bouncing.
There are a number of reasons why an email will soft bounce but generally it's because of server issues, or mailboxes being full. How many times an email is allowed to bounce before being unsubscribed is controlled by the bounce thresholds set under Contacts > Suppressed contacts > Bounce settings.
Soft bouncing can be a temporary issue (for instance, a full mailbox gets gets cleared down) and sending to these email addresses later may succeed.
Find out more about different bounce and suppression types.
Using the report
The report displays all the recipients who have soft bounced.
You can filter the list to exclude either 'soft bounces' or 'mail blocked' types.
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.