How can PHP developers troubleshoot issues with missing email content, such as the subject line, when using PHP email functions?

When troubleshooting missing email content like the subject line in PHP, developers should check if the variables being passed to the email functions are correctly set and not empty. They should also verify that the email headers are properly formatted, including the subject line. Additionally, ensuring that the email server settings are configured correctly can help resolve this issue.

$to = "recipient@example.com";
$subject = "Subject line here";
$message = "Email content here";
$headers = "From: sender@example.com\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";

// Check if subject line is not empty before sending the email
if (!empty($subject)) {
    mail($to, $subject, $message, $headers);
} else {
    echo "Subject line is empty. Please provide a subject before sending the email.";
}