Thanks for joining the Community. I'm here to address your concern with viewing sent emails from your account.
QuickBooks Online (QBO) automatically sends emails for you through Intuit's email default address firstname.lastname@example.org. However, you can view sent emails on the Sales page in your account.
Let me show you how:
Sign in to your QBO account.
Go to Sales.
Select the All Sales tab.
Click on the Filter drop down.
In the Type drop down, select Invoices. Then, choose All statuses and set the date range.
Click on Apply.
Take a look at my screenshots, so you'll know what I'm referring to.