Is there a default way to make sure all invoices are not only sent to client, but to an internal email address (accounting)?

Hi there, 

It's always good to get a copy of the invoice you send out to your valued customers. You've reached the right place as I'd be happy to show you how you can set that up. 

To do this, follow the steps below:

1. Click on the Gear icon.
2. Navigate to Account and Settings.
3. Click on Sales. Under Messages, click on the pencil icon and you'll see the option to CC or BCC your email. 

After you follow the steps above, you'll be able to email a copy of the invoice to an internal email address. 

Let me know if you have questions about this. I'll be glad to elaborate further. :)