There is no actual file that contains a list of email addresses that your board software uses for contacting the registered users in your forums. When a user selects in their preferences to receive emails when regestering under "Receive Administrator Emails" then this is what is used to determine if they get an email from your message system.
This allows for birthday email, mass emails from selected users under the member Managament search feature, and watched forums and topics as well as private message email alerts.
