User wants to create a rule to have un-deliverable status emails being forwarded to another internal email account but no definition of conditions seem to trigger the rule to start.
This is WAD.
Development intentionally added code to NOT allow the execution of reply or forward rule actions on un-deliverable status messages.
This was done to prevent looping messages.
For example, user wants to forward everything to another account.
But if, for some reason, the new account is un-deliverable, the system will be in a tight loop generating traffic.
For the case where the forwarded-to account becomes unavailable, you end up with a loop for every email received. If you got, for example, 100 new Emails before you noticed, you would have 100 email loops running as fast as the agents could process them.
Working as designed.