I've forgotten what a failed recording alert email looks like, but I don't think the notification is something which needs cancelling.
If you log into the RS, the main page for any particular machine (if you have more than one machine registered) includes a status panel showing failed recordings. This is a list of orphaned .hmt files the rs package has found and reported to RS. A .hmt file with no associated .ts file is indicative of a failed recording.
The status panel on RS offers a waste bin icon, and this queues a command to the HDR-FOX to delete the orphaned .hmt. Once the .hmt gets deleted, it will no longer be reported and listed (I think it might be removed from the list if it is scheduled to be deleted).