Your report separates messages that did not arrive at the
destination into two categories: Undelivered and Bounced. The
difference between these two types of failures is whether or not we
believe the error is correctable or not.
Undelivered messages are
soft bounces. Soft bounces could eventually be resolved. Issues such as
full mailboxes are examples of what should show up when you export your
Bounced messages are hard bounces. Hard
bounces cannot be resolved easily. A specific domain not existing is an
example of a hard bounce. For example, if you emailed
email@example.com when the email address was firstname.lastname@example.org,
this would show up as a bounced message. Addresses that result in a
hard bounce are set to inactive. We advise not re-activating hard
bounces because these email addresses are not good and will likely
never be delivered to.