Getting below error while sending mail with Magento 2.3.2:

Line <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html style="font-size: 62.5%; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; font-size-adjust: 100%; background-color: #f5f5f5;"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <meta name="viewport" content="width=device-width; initial-scale=1.0; maximum-scale=1.0;"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <style type="text/css"> does not match header format!

The Code being tried is as Below:

$toemail = "example@example.com";
$emailTempVariables = array('cid'=>$customer->getId(),'cemail'=>$email,'cname'=>$firstname.' '.$lastname);
            $senderName = $firstname.' '.$lastname;
            $senderEmail = $email;
            $postObject = new \Magento\Framework\DataObject();

            $sender = [
                        'name' => $senderName,
                        'email' => $senderEmail,

            $transport = $this->_transportBuilder->setTemplateIdentifier('email_template_identifier')
                ->setTemplateOptions(['area' => \Magento\Framework\App\Area::AREA_FRONTEND, 'store' => \Magento\Store\Model\Store::DEFAULT_STORE_ID])
                ->setTemplateVars(['data' => $postObject])
                ->setReplyTo($senderEmail, $senderName)            

Please help if someone have any idea on it.


There was an issue in header template. To resolve this issue, override header.html in your theme


and update it. I have fixed it by replacing

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">


<!DOCTYPE html>

However, more answers are welcome to fix this issue if any other best way is possible.

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