When you email a Sales Order to a customer, you can check delivery status, i.e., if the email was successfully sent and if the customer has opened the email. In QuickBooks Commerce, we call it the 'Read Receipts'.
Checking the Read Receipts
Navigate to the Sales Orders page and select the sales order that you want to email. Click on the 'Email' button on the Sales Order.

A popup with the email template will appear. Fill it in with the customer’s details and click 'send'.

To check if the email was successfully sent, refer to the activity feed on the right-hand side of the Sales Order screen. You will see a tab that reads 'Show History' when you scroll down. Expand the tab to see details of the activity, e.g., an email has been sent.

You will see that the email was sent. When the customer opens/reads the email, the status within this box will be updated according to the time stamp. Now, click on the activity to see the status of the email.

