When you are distributing a newsletter you need to add a link to an opt-out form.
To see how to create an opt-out form click here.
How to add opt-out form to your email
Step 1. To add the opt-out form to your subscriber options text you simply right click on the footer widget, mark the text and click on the insert link button.
Step 2. Then you add the unsubscribe tag. Protocol should be set to <other> and the URL should have the merging code [unsubscribe].
Step 3. Under "Style" section you can choose what form should be attached to the merging code.
Click on "Save" button when you are done and you are ready to distribute.