For reservation notifications:
Go to Menu > Settings > Services > Bookable services > Choose respective service (e.g. Stay) > Options
Tick off the options which make a new order generate an email or a notification:
You can also adjust the Responsible Employee or department by scrolling down to the Responsibility section
This is the department or employee that will be notified by new reservations:
For Mews Payments notifications:
Head to Settings > Marketplace > My subscriptions > Merchant settings. Change the notification email for merchant notifications as well as the email which will be receiving chargebacks.