__OPTOUT__
as in : 'underscore-underscore-OPTOUT(call-caps)-underscore-underscore'
The system will then upload all of the addresses and add them to the suppression list for that profile.
you can then delete that list as the suppression has already been actioned!
If the customer decides not to delete the optout list. They can add more addresses to optout to it by appending it. This will also optout the address