When you are trying to get your email verified in order to send pre order emails from your email, you need to get it verified with Pre order now's ESP.
To do so:
Go to Pre order now's Settings, then click on the Email tab and enter the email you want to verify in the Email from address section:
Click on verify button and open the inbox of the respective email.
Look for an email like below:
Click the larger link to verify your email and that should be it! Open the app and refresh to check the confirmation status.