drupal on fasthosts won't send email

Ok, I'm new to drupal but I set up an email action to email me and associated it with a new comment. Then I added a comment as someone else and no email arrived. Then I found Using Drupal's email address in the mail.inc main function with -f which seemed to suggest the from address must be set if you are on fasthosts. Anyway the patch provided to mail.inc worked just fine. I include it here, partly as a reminder to me that I made this change:

--- mail.inc.orig 2008-01-25 17:04:00.000000000 +0000
+++ mail.inc.new 2008-04-05 20:35:52.991525652 +0100
@@ -181,13 +181,19 @@ function drupal_mail_send($message) {
foreach ($message['headers'] as $name => $value) {
$mimeheaders[] = $name .': '. mime_header_encode($value);
}
+
+ // added 5.4.08
+ // fasthosts needs -f parameter
+ $from = variable_get('site_mail', ini_get('sendmail_from'));
+
return mail(
$message['to'],
mime_header_encode($message['subject']),
// Note: e-mail uses CRLF for line-endings, but PHP's API requires LF.
// They will appear correctly in the actual e-mail that is sent.
str_replace("\r", '', $message['body']),
- join("\n", $mimeheaders)
+ join("\n", $mimeheaders),
+ "-f$from"
);
}
}

BTW, I can find an API reference to variable_get and can see it gets 'site_email' and defaults to 'sendmail_from' but where the hell would 'sendmail_from' actually go assuming I wanted a different email address to the 'site_email'.