Hello, BlackInk3200. 

I would also want to be efficient in keeping track of my lists. I'll shed some light on how the emailing system works in QuickBooks and help you manage your customer's email addresses. 

The invoices and statements will go to the email entered in the customer profile. We're unable to specify where a specific email address would go at this time. 

To keep track of your customer contact information, you'll want to run the Customer Contact List report. Simply go to the Reports menu, then search "Customer Contact List" in the search box. 

Also, you can enter another email address (the accounting office email in this case) in the customer profile. You'll want to add a comma to separate the main and the office email addresses. Here's how:

1. Go to your Customers list in QuickBooks Online.
2. Find and select your customer.
3. Click the Edit button.
4. In the Email box, enter the accounting email address (separated by a comma). 
5. Click Save.

Do this to the rest of your customers. When you send a statement (or any transaction), it will be sent to the main and the accounting office email addresses. 

Our engineers might change the flow and add more features on how you'll be able to email customers (and vendors). You'll want to check out our QuickBooks Blog for future releases and new updates. 

Do you have other tasks to tend to in QuickBooks? Our help content can definitely help you out. Browse them in our articles list page and look for an article. 

Let's hear your other concerns if you have any. I'm willing to help you out in completing your tasks in QuickBooks.