What common error message related to the mail() function in PHP indicates that "sendmail_from" is not set in php.ini or a custom "From:" header is missing?

The common error message related to the mail() function in PHP that indicates "sendmail_from" is not set in php.ini or a custom "From:" header is missing is "mail(): You must provide at least one recipient email address." This error occurs when the email headers are not properly set up to include the sender's email address. To solve this issue, you need to specify the "From:" header in the mail function with a valid email address.

$to = "recipient@example.com";
$subject = "Test Email";
$message = "This is a test email.";
$headers = "From: sender@example.com";

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