The notification set up on your accountant's payroll profile needs to be configured on their end. Doing so, they can only receive email notification needed.
Please have your accountant login to QuickBooks and disable this option on their notification settings. Here's how:
Go to Employees tab.
On Manage Employees drop-down menu, select Notifications.
Untick Email me when an employee that I supervise requests an expense reimbursement.