headerLine example

//createBody may have added some headers, so retain them             $tempheaders = $this->MIMEHeader;
            $this->MIMEHeader = $this->createHeader();
            $this->MIMEHeader .= $tempheaders;

            //To capture the complete message when using mail(), create             //an extra header list which createHeader() doesn't fold in             if ('mail' === $this->Mailer) {
                if (count($this->to) > 0) {
                    $this->mailHeader .= $this->addrAppend('To', $this->to);
                } else {
                    $this->mailHeader .= $this->headerLine('To', 'undisclosed-recipients:;');
                }
                $this->mailHeader .= $this->headerLine(
                    'Subject',
                    $this->encodeHeader($this->secureHeader($this->Subject))
                );
            }

            //Sign with DKIM if enabled             if (
                !empty($this->DKIM_domain)
                && !empty($this->DKIM_selector)