Email bounces are automatically processed by Lead Liaison. After processing your emails, subscribers will be marked appropriately, and you can access all bounce related statistics from the Reports > Standard > Emails section.
Hard bounces will mark a Subscriber as "Bounced" by the application after one bounce, and deal with problems like "email address doesn't exist" or "invalid domain name". Soft bounces deal with more common problems like "relay problem" or "mailbox is full". In case of a soft bounce our system tries to send the messages for 3 5 days. Attempts decrease over this time period (several delivery attempts during the first hour, then a couple times only during the 3rd day, etc.). After 5 days we do not report the email as being a hard bounce.