PHP/Cronjob Mail Function [duplicate]

I have a website on the web, and I want to use CronJob, to send newsletters every Monday.Now, I'm using PHP to do this, and I'm stuck.I have a mail() function, that sends mail, to every address stated in a file.

Here is my CronJob file. I changed the date to everyday, just for debugging.

0 9 * * *   php -f /home/a4770799/public_html/mail/newsletter.php

Here is my PHP file. This is the whole file.

<?php  $subject = "Weekly Newsletter";  $msg = "This is a weekly newsletter debugging test.";  $headers = "From: noreply@test.com" . "\r\n" ."Reply-To: example@test.com" . "\r\n";  $linesofmail = file("mail_address_list.txt");  foreach ($linesofmail as $line_num => $line) {    mail ($line, $subject, $msg, $headers);  }?>

What might be the problem here? I would love it, if someone would explain the problem to me, instead of just giving me a piece of code.