alarm

I am using Rules to send a reminder for cases in open atriums case tracker based on a date field. I came quite far (http://drupal.org/node/652158), but I'm having trouble sending the mail to the right user. Right now, the mail goes to the author of the node. I would like it to go the assigned user for that case however. The assignee is not a content field, but a custom value created by the case tracker module. In views I can use case tracker fields, but the case tracker context doesn't show up in the rules argument data type list.