How can I see the emailed messages that I have sent to clients that accompanied invoices I have sent in the past?

Hi parkersusanrenee, 

Sending customers their invoices directly from QuickBooks Online is so convenient. It will make your task that much easier, without you having to export the invoice to your computer and attach it to an email outside the system. If you're busy sending tons of invoices, it's easy to lose track. I'd be happy to explain a few tips on how to manage sent invoices. 

The first thing you can do to keep track of sent invoices is to refer to the Invoices list. Click the Sales tab on the left menu, then select Invoices. In the Status column, QuickBooks will tell you which invoices have been sent and which ones haven't. Keep in mind, this will only apply to invoices that haven't received payment yet. Paid and deposited invoices won't specify whether they were ever sent to the customers.

Here's a screenshot of what you'll see in the Status column:

Another way to keep track of the invoices you've sent is to Cc yourself on each email. This will send both you and your customer a copy of the email so that you can feel confident in which emails have been sent, and which ones haven't. To add yourself as a Cc on the email, open the invoice and click the Cc/Bcc tab under the email field. Add your own email there.

Here's what that looks like:

I hope this helps.

Have a great day!