When we send an invoice it's possible to receive a note in QB that it's been read. However, this isn't the case for Estimates and I believe it'd be beneficial if it was.
As it is not Quickbooks but your email provider that actually sends the invoice, it is not possible to request a read confirmation in QB. However , if the Invoice is sent using the email function in QB Desktop Program, there will be an email sent confirmation in the Customer Information pane.
For now, the option for you to know if the estimates was been read by your customer isn't available in QuickBooks. I know the importance of this option in running your business. I'll make sure to send feedback to our developers so they review this one and probably add this feature in any future updates.
In the meantime, you can also check our Firm of the Future website to stay in the loop when it comes to product developments.
If you ever have other questions we can help you with, feel free to swing by the Community!