Just too bring this thread to a conclusion.

add_action( 'fep_message_table_bulk_actions', function(){
$filters = array(
'delete' => __( 'Delete', 'front-end-pm' ),
'mark-as-read' => __( 'Mark as read', 'front-end-pm' ),
'mark-as-unread'=> __( 'Mark as unread', 'front-end-pm' ),
'archive'=> __( 'Archive', 'front-end-pm' ),
'restore'=> __( 'Unarchive', 'front-end-pm' ),
);
return $filters;
});