Primebox will retrieve replies from all contacts in your Salesforge contacts list, regardless of whether those contacts are currently in a sequence or not.
Also all replies from @company.com will be fetched, meaning if you have tom@google.com in your contacts list, then replies from anyone from @google.com will the fetched too regardless if that other person is in your list or no, so if ana@google.com replies, you will see that reply in Primebox even if ana@google.com is not in your list because tom@google.com is in your list.