It is possible to blacklist a contact from your Sarbacane Engage inbox when you are processing the replies you have received following the sending of your prospecting sequences. You must select the reply from the prospect concerned and follow the described procedure to add a contact to the blacklist from the contact record. Indeed, a mini-record appears on the right once you have selected the reply from the contact concerned.
Two other options are also available to you to populate your prospecting blacklist
Populate the blacklist via the Sarbacane Engage settings
Add a contact to the blacklist from their contact record