Does someone know why quickbooks is sending remainder emails to the customers on my company ?

I know what's happening here, JS pool.

QuickBooks Online checks the due dates on your invoices a few times a day. The program automatically sends reminders to those customers with Overdue invoices. In addition, you can't exclude specific customers.

I'd recommend review the due dates of the invoices and correct it if necessary.

1. Click Sales on the left menu and go to the Invoices tab.
2. Under the STATUS column, open the invoices with Overdue statuses one at a time. 
3. Click Edit invoice and change the Due date if needed.
4. Click Save and close.

You can also browse this article for more information about the automated reminder: Automate invoice reminders in QuickBooks Online.

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