The Email Campaigns Preferences screen can be accessed from your dashboard by clicking on the ellipsis (...) on your Email Campaigns App and selecting Preferences.
When you create the email content for your campaign, you are asked if you want to include a default opt-out message at the bottom of the email.
The preferences menu allows you to customize the default message that appears when you open the Create Email Content screen. You can still edit the message within that screen.
Click Save to save your changes. These preferences will take effect immediately.