Email notifications are sent out from Chargebee to the email address present in the customer's account information whenever an event occurs. So if your customers request that you send the notifications to another email address as well, you can do that. Just add them as an Additional Contact to the customer record.
To do this, log in to the Chargebee web interface, navigate to Subscriptions -> Customers -> Open customer record -> Additional Contacts, click Add Contact. Screenshot is below:
As per your requirement, check 'Billing Emails' and/or 'Account Emails' so that the respective email notifications are sent to the additional contact as well.
Alternatively, you could create an additional contact for a customer using the 'Add contacts to a customer' API. With this API, pass the contact[send_billing_email] and contact[send_account_email] parameters as true or false depending on the email notifications that you'd want the additional contact to receive.
1) The first email notification during signup or when creating a new Customer can't be sent to the additional contact because an additional contact can only be added to an existing Customer.
2) You can add upto six additional contacts for a customer.