You can configure an automatic unsubscribe to accompany all of your messages by going to Settings then Account, and clicking the edit icon next to the Automatic Unsubscribe option:
Here you can specify:
1. The keywords you want to use for Opt-Out messages
2. The content of the automated opt-out message
3. The Unsubscribe link message
Once you have configured your messages, they will appear when you click on the button to add an Unsubscribe message to your message content:
For more information about opt-out regulation and compliance, read this article