src/MailMap/Mail.php
public function header($key, $default = null)
    {
        if (array_key_exists($key, $this->headers)) {
            return $this->headers[$key];
        }

        return $default;
    }
public function header($key, $default = null)
    {
        if (array_key_exists($key, $this->headers)) {
            return $this->headers[$key];
        }

        return $default;
    }
public function header ( $ key , $ default = null ) { if ( array_key_exists ( $ key , $ this -> headers ) ) { return $ this -> headers [ $ key ] ; } return $ default ; }
Get a header value. Return given default if none found

@param  string $key
@param  mixed $default
@return mixed
Get a header value . Return given default if none found