private function buildHeaders() {

		$this->headers = [
			'From' => $this->sender,
			'Return-Path' => $this->sender,
			'Reply-To' => $this->sender,
			'Date' => (new \DateTime())->format('r'),
			'Message-ID' => '<'.sha1(microtime()) . '@' . substr($this->sender, strpos($this->sender, '@') + 1) . '>',
			'User-Agent' => 'vxPHP SmtpMailer',
			'X-Mailer' => 'PHP' . phpversion(),
			'MIME-Version' => '1.0'
		];

		if(!empty($this->cc)) {
			$this->headers['CC'] = implode(',', $this->cc);
		}

		if(!empty($this->bcc)) {
			$this->headers['BCC'] = implode(',', $this->bcc);
		}

		if(count($this->attachments) > 0) {
			$this->boundary = '!!!@snip@here@!!!';
			$this->headers['Content-type'] = sprintf('multipart/mixed; boundary="%s"', $this->boundary);
		}
		else {
			$this->headers['Content-type'] = sprintf('text/%s; charset=%s', $this->htmlMail ? 'html' : 'plain', $this->encoding);
		}

	}