Hi,
Actually, my expectation would be that the work item is in error status if no agents were found (as described in KBA 1850076). Did you check under "Agents" -it corresponds to the selected agents - marked yellow?
You also might check KBA 1846041 - it contains further information on troubleshooting ERMS Inbound E-Mails.
Also for example an explanation on how to use transaction CRM_ERMS_LOGGING for debugging. This allows to debug the rule evaluation.
Additionally, you might check in the E-Mail Workbench - there you see better formatted information than in SWI1.
Best Regards,
Sigrid