User macros should be evaluated also in the action message. It's common place to mention a disk drive {$DISKDRIVE0} both in the email message subject and the message body. User macros are currently resolved in the email message subject but not in the message body.

The same issue with the graphs->graph dropdown list – you have a graph named "{$DISKDRIVE0} disk latency" and that does not get resolved in the list of graphs you can choose from.