public function addMetadata($data)
    {
        if (is_array($data)) {
            foreach ($data as $k => $v) {
                $this->metadata[$k] = $v;
            }
        }
        else {
            $this->metadata[] = $data;
        }

        return $this;
    }
public function addMetadata($data)
    {
        if (is_array($data)) {
            foreach ($data as $k => $v) {
                $this->metadata[$k] = $v;
            }
        }
        else {
            $this->metadata[] = $data;
        }

        return $this;
    }
public function addMetadata ( $ data ) { if ( is_array ( $ data ) ) { foreach ( $ data as $ k => $ v ) { $ this -> metadata [ $ k ] = $ v ; } } else { $ this -> metadata [ ] = $ data ; } return $ this ; }
Add global metadata.

Mandrill will store this metadata and make it available for retrieval.
In addition, you can select up to 10 metadata fields to index and
make searchable using the Mandrill search api.

@param string|array $data

@return Message
Add global metadata .