Can the customer email changed automatically after system update their email address

Hello, @infiniteesg.

I'm happy to assist you with your customer inquiries in QuickBooks Online (QBO).

Yes, the system will automatically save any changes you make to your customer's profile after updating their account details. When you edit customer information, the changes will be reflected in other areas of your company file, including previously sent invoices. QuickBooks also updates any recurring templates that use previous information, such as billing, shipping, and email addresses, as well as the preferred payment method and terms.

Here’s how to edit a customer’s info:

1. Go to Sales and select Customers.
2. Choose the customer you want to update.
3. Click the Customer Details tab.
4. Select Edit.
5. Make any changes.
6. Select Save.

For additional info, you can check out this article: Add and manage customers in QBO. 

You might also find these articles helpful in achieving basic tasks in the program:  Video tutorials for QuickBooks Online.

Please don't hesitate to reach out if you have any further questions about managing your customer's account in QuickBooks. I'm here to help. Take care.