Duplicate Email can be found in Theme Options-> Email Management -> Duplicate Email 

What it does:

Any email address you enter here will receive a copy of every email sent by the theme — including messages like:

• New booking requests

• Contact form submissions

• Payment confirmations

• Messages between users

• Admin notifications

This is useful for admins, site managers, or backup purposes, so no important communication slips through the cracks.

Learn more:

For a complete list of notifications and how they work, check the documentation here:
👉 Theme Email Notifications – WpRentals Help