What is the field name that accompanies the To Be Emailed checkbox on transactions?

I need the field name (hopefully it is available in Saved Search) that holds the email address that accompanies the To Be E-Mailed checkbox.

I need to clean up our database and clear the To Be Emailed, email addresses but need to get the field on a Saved Search so I can determine which are no longer valid then do a .csv upload to clear them from the Invoices.

We are using the Invoice Renew Button to create an Estimate. We update the Estimate and send through our approval process. After the Estimate is approved, we create a Sales Order, then the Invoice. We manually send invoices to the current customer AP contacts. Because our Estimate is a copy of the invoice, and the invoice had an old email address in this To Be E-Mailed address field, the new invoice inherits the old email address.