Thank you for being one of our QuickBooks family for three (3) years, @apsdynamics. I appreciate you using the recommended operating system to get the most out of QuickBooks. Know that we listen to your sentiments about having the same issue with everyone in this thread.

I understand you've made no changes to your operating conditions and have no recurring transactions. Therefore, the email duplication issue when sending Invoice Reminders and Estimates is an odd behavior.

Sales forms are critical for customer communication. I agree that receiving two emails with the same information may cause confusion that affects the vendor-client relationship. To resolve this, I recommend contacting our Support Team. They can help figure out the reason behind this and provide resolutions.

Here's how:

1. Go to the Help icon and choose Search.
2. Click the Contact Us button and enter your concern.
3. Press Continue.

For more tips on enhancing or personalizing sales forms, refer to this guide: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Once everything is settled, you can check out this reference for the complete details of receiving payments: Record invoice payments in QuickBooks Online.

Our Support Team is willing to assist you in sorting out this duplicate email issue. If you need help with handling your receivables, add them below. We're always here to help you.