By default, Yesware will sync email activity to the Contact or Lead record with an email address that matches the email address of your recipient (what happens if there are duplicates?). If the recipient's email address is associated with a Contact, it will also automatically sync to the Account record in addition to the Contact Record.  

If, and only if, the Contact is assigned as a "Contact Role" on an open Opportunity, Yesware will automatically associate newly sent emails, as well as replies, opens, and link-click events from that Contact, with the Opportunity. Click here to view Salesforce's instructions on how to set up Contact Roles in Salesforce. 

Once you've assigned the Contact as a Contact Role on an open Opportunity, Yesware will now automatically sync email activity to the Contact record, the Account record, and the Opportunity record.