You'll have to open the estimate transaction, so you can see the email sent from your QuickBooks account. I'll show you how:
Go to the Sales menu then select All Sales.
Click the Filter drop-down.
Under Type choose Estimate and filter the necessary details.
Open the estimated transaction to see the email details below Customer.
To check the details of your Estimate click More at the bottom then Audit History.
Tap the History of this transaction.
You can also run the Estimate by Customer report. This report will provide you the name of the customer, estimate number, and other information. Just click the Reports tab then search Estimate by Customer report.
I've included these articles that will guide you on how to personalize your sales forms and email it to your customer within QuickBooks Online: