If a survey is sent to someone in your employee email manager and the email bounces back, that email address will be moved to the Invalid Employees tab. No further emails will be sent to that email address.
You can correct theses email addresses by clicking the Fix Employee option next to the email address and entering the correct email address. In this example, firstname.lastname@example.org should actually be email@example.com.
Once you input the correct email address and select Add, the corrected email address will be added to your employee email manager and the incorrect email address will move below and be shown as a corrected email address.
If you click over to the Employees tab, you will now see the corrected email address of firstname.lastname@example.org available.
You can send the survey directly to any corrected employee email addresses by following the steps listed here.