Sometimes, when emailing a prospect from a campaign, the person will have an automatic out of office / vacation responder. In these cases, you will receive an email in your inbox, but it is not a reply.

When we see emails like this, we don't mark the prospect as finished or replied. Instead, we pause the prospect.  

You can see paused prospects by navigating to the prospects tab of your campaign. 

At any point, you can resume the prospects in the campaign