I guess all I needed was a sprintf command joining the $body with each additional user for which quota data was collected:

$body = $body . sprintf ("$user\'s disk usage \= %.2f MB.\nHas %.2f MB
+ available.\nQuota se
t to: %.2f MB\n\n", $used, $remainingquota, $limit);</BOLD>
[download]

Now I get the emailed quota data.
Thanks for the reponses, Chris