No, Evercontact does not create duplicates--- in its first version, it used to create a new contact for every email address, but based on user feedback, we've improved this.

As of 2015, here's the process: 

  1. Evercontact detects an email signature & compares this email address (both the email address mentioned within the signature + the email in the from:) to find that email address within the contacts in your address book. 
  2. If no contact matches that email address, then Evercontact looks for a contact with the same name (first name & last name). 
  3. If still there is no contact match, then we create a new contact.

There is of course a chance that contacts with the same name may be merged, but most times, their emails will match up before this will happen & we've received zero feedback about this negative possible outcome.  In general, this process is similar to Gmail's "merge" function which you can read more about here: