Unsubscribe contacts from csv. The CSV format is "email" and "externalCode" is optional.

  email,externalCode
  [email protected],ext1

  email
  [email protected]

If the contact already exists, their unsubscribeAll field will be set to true. If the contact does not exist, it will be created with the unsubscribeAll field set to true. The externalCode will only be set for new contacts and is optional. In the case of repeated emails with different externalCode values, only the last entry will be preserved.