Custom Notification Email limited to users

Hi,

It seems these are limited to send emails only to users, and does not allow us to send the notification to an email address which is listed as a field on the sheet.
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When a record is approved we would like to email external parties without adding them as users and do not want the users to have to click a button as they will sometime forget and often approve from within the approval email.

Please can you help?

Regards