To validate a Campaign email address:

How to validate the Campaign email address ?

1. Go to Setup > Marketing > Setup Tasks > Email Addresses.
2. Click Edit next to the email address you want to validate.
3. In the Authentication Code field, enter the code included in the email NetSuite sent when you saved the record.
4. Click Save.

Note: In production account the authorization code will be send to the mail address created as the campaign email address, whereas in sandbox and release preview accounts the code will be send to the mail address mentioned in the Email Preferences.

You can select a validated email address on campaign email templates to serve as the From address, the Reply to address, or both.