Hard Fail = the e-mail cannot be delivered (many possible reasons) Typically, the recipient address does not exits.
Soft Fail = temporary technical reason why the e-mail is not delivered to the receiving mail server. (many possible reasons) Typically, the sender is temporarily blacklisted.
Bounced = the e-mail can not be delivered the user mailbox or the user has rejected the message. (many possible reasons)
In both cases the sender (Polaris) will try several times to re-send the message after some time. The number of repetitions and the timeouts depend on the configuration and are quite complex.