As of 5/1/17 ToutApp will append a block unsubscribe link on any group email over 20 contacts. [A block unsubscribe prevents anyone in your Tout subscription from emailing that Contact and it updates Salesforce with an opt-out]
This is not something that can be removed from emails because it avoids getting Spam complaints and our servers from being blacklisted. Additionally, it helps our users with inbox placement and to avoid bounces.
Sending bulk emails without unsubscribe links is a big red flag for our email providers, email filters, as well as the blacklist companies. If you don't want to have the unsubscribe link added, you will need to send in groups of 19 or less.
You can update the content of the link in your Unsubscribe Settings.