Form email is not successfully sent, but there is no log (or is there?)

I have turned on logging in /etc/php5/apache2/php.ini by enabling error_log = syslog and before that I had error_log = php_errors.log, but nothing is logged regardless of whether email can be sent from a form or not.

If while file is the email sending code?

Thanks Josue,

The code is:

 if($use_wpmail)
                                {
                                        $header .= 'From: '. $from . " <".$from."> \r\n";
                                        wp_mail($send_to_mail, $subject, $message, $header);
                                }
                                else
                                {
                                        $header .= 'From:'. $from . " \r\n";
                                        mail($send_to_mail, $subject, $message, $header);
                                }

Now I have two questions: How can I add something in here to make this thing log what it tries to do, since it doesn’t send the mail?

Then, while were at this point:

The $header variable contains the $from strong (email address), but I want to it to also contain the address that the person entered in the form so that when I hit reply in the email that I receive from wordpress, the mail will be sent to the person that filled in the form. How can I add a “reply-to:” header in there and what is the variable that contains this address?

The php mail function has this example:

<?php
$to      = ' (Email address hidden if logged out) ';
$subject = 'the subject';
$message = 'hello';
$headers = 'From:  (Email address hidden if logged out) ' . "\r\n" .
    'Reply-To:  (Email address hidden if logged out) ' . "\r\n" .
    'X-Mailer: PHP/' . phpversion();

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

So in this example, how to I add the add the email address that the enquirer entered in the form as the reply-to address?