Add to existing record based on email unique ID via web form.

Add to existing record based on email unique ID via web form.

Hi All. I'm completely new to Creator and loving it! 

I'm trying to use Creator to build a very simple CRM and recruitment solution (I've already checked out Recruit).

My scenario is as follows

1. User submits registration form on website where their email address should be treated as the unique id (I have step this working no problem)
2. User comes back to website and expresses an interest in a job, Creator should add this expression of interest against the person's record based on identifying them by email address.

So the question is, how can I get Creator to ADD to an existing record based on being identified by their email address, else, create a new record?

Thanks in advance.
S