Can I retrieve a sent email to check it?Can I set a default, for a copy of an invoice or quote email to come to me?Can I set the invoice default to Payment on Receipt?

Thank you for taking the time to reach out to us here on the Community page, @anitamac49.

We won't be able to retrieve transactions that are already sent out from QuickBooks Online (QBO). However, you can open them within QBO and check the details from there.

On the other hand, yes, you can set a default email for a copy of an invoice or quote that'll be sent to yourself. This can be done by following these steps:
 

1. From the Gear icon, select Account and Settings under Your Company.
2. Tap on Sales at the left pane.
3. Click on the pencil icon beside the Messages.
4. Select a sales form under the Sales from section, then put a check-mark on the box beside Email me a copy.
5. Enter the email address/es under Copy (Cc) new invoices to address or Blind Copy (Bcc) new invoice to address.
6. Hit Save, then Done.

For additional reference, you can read this article: Email a sales form or report to multiple email addresses.

Lastly, paying invoices usually depends on the payment method selected when creating the invoice. To learn more about paying invoices, you can check out these articles:

• How to pay your Invoice sent from QuickBooks
• How to add a Pay Now button to an invoice
• Common questions about paying invoices online

Let me know if you have any other questions and clarifications. I'm always here to help. Have a good day ahead!