What best practices should be followed when including HTML content in email messages using PHP?

When including HTML content in email messages using PHP, it's important to properly format the HTML code to ensure it displays correctly in email clients. This includes using inline styles, avoiding external CSS files, and testing the email in different clients to ensure compatibility. 

// Example PHP code snippet for sending an HTML email
$to = "recipient@example.com";
$subject = "HTML Email Test";
$message = "<html><body>";
$message .= "<h1>Hello, this is a test email!</h1>";
$message .= "<p>This is some sample content in the email.</p>";
$message .= "</body></html>";

$headers = "MIME-Version: 1.0" . "\r\n";
$headers .= "Content-type:text/html;charset=UTF-8" . "\r\n";
$headers .= "From: sender@example.com" . "\r\n";

mail($to, $subject, $message, $headers);

Keywords

PHP email messages HTML content security validation

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