Hi everyone,
Marketing email reply tracking across HubSpot is currently in beta. Included with this new feature, are additional list criteria related to marketing email replies. This means that marketing email replies can be used in workflow supression lists or as workflow goal criteria, for the purpose of unenrolling contacts who have replied to certain marketing emails 
Please follow this thread for the most up to date information about that beta:
https://community.hubspot.com/t5/HubSpot-Ideas/Email-Reply-Tracking/idi-p/2594/page/8#
Best,
Megan