When a contact or email recipient sets an away or out of office message, sometimes this is registered as a soft bounce.  It can also sometimes be registered as "delivered" or you may receive a response in your reply to email address.  This is because sometimes servers don’t recognize the reply-to address in an email, or can be largely dependant on how the "away" message is set.

Not all mail servers are able to recognize the "reply to" or "from" address though and so the message is sent to the bounce address in the campaign (the address that Benchmark Email inserts into the campaign to receive bounces). Those are kept in the Benchmark Email bounce manager so that you are aware your campaign was returned.