Email bounce has categorize in two category, which is hard bounce and soft bounce. A soft bounce email referring to recipient mail server temporary rejection, automatically attempt action shall carry out by sender outgoing mail server. In default Ebuzzzzz bounce setting, more than 3 times of soft bounce will be categorize as hard bounce. Hard bounce in email deliver is referring to permanent rejection, one of the good example is intended recipient email does not exist under destination server.
To be more precise on differentiate both category, may refer to PDF document below.