A "Hard Bounce" is a bad email address. A hard bounce is a permanent event like blocked email or email doesn't exist. A "Soft Bounce" is typically a good email address, but spam filters and/or email firewalls prevented your email from being delivered.
A soft bounce is primarily something that is temporary like an out of office reply, mailbox is full, recipient mail server is down or email message is too large. We do not offer any guarantee on "Soft Bounce" rates for the above stated reason.