Change default from address to sharing-noreply@server for emailing private links

apps/files_sharing/ajax/email.php

@@ -6,7 +6,7 @@ $user = OCP\USER::getUser();
 $subject = $user + ' ' + 'shared a file with you';
 $link = $_POST['link'] + '&f=' + $_POST['f'];
 $text = $user + ' ' + 'shared the file' + ' ' + $_POST['f'] + ' ' + 'with you.' + ' ' + 'It is available for download here:' + ' ' + $link;
-$fromaddress = OC_Preferences::getValue($user, 'settings', 'email', 'owncloud.org');
+$fromaddress = OC_Preferences::getValue($user, 'settings', 'email', 'sharing-noreply@'.$_SERVER['HTTP_HOST']);
 OC_Mail::send($_POST['toaddress'], $_POST['toaddress'], $subject, $text, $fromaddress, $user);
 
 ?>
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