To

This property is used to name the field (column) in the form that is used to determine the email address to send the email to.

To append an email address to a selection box from within your field, place the email address within brackets [ ]. Example: Approval Required [approver@company.com] The web part will parse out the email address when the notification is sent. You can also utilize a single or multi-line text field that allows users to enter email addresses manually.