When I send out a campaign, sometimes I personally receive automatic messages about subscribers on vacation or their mailbox is full. Why didn’t those messages go to the Benchmark Email bounce report?

When someone sets up an "auto-reply" message, this will be registered as a soft bounce when they are returned to Benchmark Email. However, some auto-reply messages are returned to the address that is specified as either "from" or "reply-to" in your campaign. This is why you would see them in your inbox rather than in the Benchmark Email reports tab. Not all mail servers are able to recognize the "reply