I understand that you're looking for a quick solution to update the email addresses of your existing customers in bulk within QuickBooks Online (QBO), Vidya.
Updating existing customer information, such as email addresses, in QBO through an import or bulk upload is unsupported. The import functionality is designed primarily for adding new customers to your account.
To ensure the email addresses for your existing customers are accurately reflected in your customer profiles, I recommend updating them manually.
For a detailed walkthrough, here's how:
- Navigate to the Sales menu and choose Customers.
- Select each customer whose email you need to change and click their name.
- On the customer's profile, click the Edit button.
- Update the email address in the Email field.
- Click Save.
You can quickly find the customers you need to edit using the search bar located at the top left corner of the customer list.

Feel free to ask if you need clarification on these steps or help with any other tasks in QBO.