If you need to restrict the ability for users on your account to email invoices and payment receipts to patients, you can do so in the Patient privacy section of Cliniko.
To turn it on, first head to Settings, and then Patient privacy:
Under Patient financial data, make sure to tick the box next to "Prevent emailing invoices and payments":
Save the settings, and you'll be all set. 👍
With this setting turned on, no one will be able to email invoices or payment receipts from Cliniko. This will not prevent a user from downloading or printing a copy of the invoice or payment from Cliniko, but rather, will not display the "Email" button on the invoice or payment when viewing it.