Thanks for getting back to us, @RachieB.

I'd like to share some follow-up information and make sure to help you complete the tasks. 

To start, let me clarify a few things too. Are these invoices have been sent out already? If this is what you mean, they'll no longer show as being sent from the new email address. Those transactions can only be viewed from the old email address. 

The new email address will reflect the invoices that have not yet been sent out. Still, QuickBooks will automatically generate the new email address to all transactions (only for recording purposes). You may consider deleting and recreating them. 

Still, I recommend checking the articles shared by my colleagues above. You'll surely get tips and details about managing emails in your QuickBooks account.

Also, you can check this link to get more details about managing QuickBooks Online: QuickBooks Q & A.

Please let me know if you're still referring to something else. We're always here if you have follow-up questions with your current concern or need anything else with QuickBooks. Take care, Rachie.