Hello there, lisacslater. 

The option to view the communincation status in QuickBooks Online is seen the Invoices page. Go  to the Sales menu and click Invoices. The option to see if what email that have gone back and forth is unavailable. 

You can review the status from there and see if it was Undelivered or Not sent so you can resend the Invoice again. If there were changes made to the transaction after it was first email, you can use the Audit Log report to check the original details.

My colleague already sent a feedback about your suggestion and I've notified our engineers again. 

I'll be here if you need more help!