What if I don't want data syncing back to Salesforce from Delivra?

Under the "ESP-TO-SALESFORCE" settings, you can set the dropdown next to "New contacts should" to "not be added to Salesforce". This answers the question, “When a new contact is added in Delivra, should they be added as a Lead or Contact in Salesforce, or not added at all?”, so it will prevent Delivra from sending new contacts to Salesforce:
 

 
On the navigation bar on the left hand side of your screenshot, there is a "LEADS" option. That is where the mapping takes place and you can select the "one way: Salesforce to ESP" option so that Delivra is NOT updating Salesforce. Data flows from Salesforce to Delivra only when that option is selected: