CRM Contacts ---> Outlook

A client updated a Contact in CRM.  It apparently created a new Contact in Outlook for him.

Now he's thinking that is why they have so many Duplicated Contacts in Outlook.

I am aware of synchronized fields settings in Outlook, but not how to prevent creation of CRM Contacts. In other words: it is possible to set Outlook to NOT create a new contact when an CRM contact is being updated?