How do you "turn-off" the Customer email and emailing of the invoice in QBs Online?

Hello there, @cwallner.

You can turn off the customer's email from the Customer Information page. However, once removed you can no longer email that customer. 

To turn off the customer's email, here's how:

1. Go to the Sales, then click the Customers.
2. Select the customer name and click on Edit at the top right corner. 
3. From the Email section, remove the Customer's email.
   
   
4. Click Save, once done.

Also, I've attached this article below to learn more emailing sales forms and expense receipts in QuickBooks Online for reference:

• How to email a sales form or report to multiple email addresses.
• Email receipts to QuickBooks Online.

Don't hesitate to let me know if I can be of additional assistance. Cheering your business to continued prosperity.