Email responses as in replies? No, because Marketo does not process replies.
Email responses as in opens and clicks? Yes, to a limited degree. This is covered in the docs under Customize Activities Sync - Marketo Docs - Product Docs
Unfortunately you cannot sync the response in a reply email directly back to MKTO or SFDC.
However, if you do use the Sales Insight plugin you can log an incoming email (there should be a button that appears once you install it). That will log it back to that lead/contact's record in SFDC.
Hi Danielle - I had a similar situation at a previous role. We sent out a large volume of automated sales 'from-rep' emails with CTAs of 'contact me'. To report on these direct responses I simply had our Salesforce team create a custom field Direct Reply on the lead/contact record in Salesforce that we mapped back to Marketo. Reps would update the field when they fielded a direct reply, and we could then run reports that would attribute the direct reply back to the most recent campaign to see what email copy was driving the most direct replies.