Hello,
The below link will give you step by step process for configuring workflow for idoc failures. Please note it doesnt send an email when inbound/outbound idoc fails, instead it send a work item in SAP SBWP inbox of post processing agent maintianed in partner profile.
http://www.****************/Tutorials/ALE/ErrorHandling/Index.htm.
@Rick: As per my knowlegde, it doesnt trigger event in case of idoc with workflow.
Regards,
Ibrahim