Method to add localparts to the suppression list.
https://api.wbsrvc.com/SuppressionList/ImportLocalparts/
POST
| user_key Required |
User Key of the user who initiates the call. Type: string |
| localpart Required |
List of localparts. Type: array of localparts - i.e. array('info') |
| client_id Optional |
ID of the client. Type: integer |