Let's say that someone neglected to set up the Listener operator account, or set it up with the wrong password, and the EmailListener record is not similarly updated.
Here's the error shown in SMA to your system admin trying to start the Listener:
Listener 'Data-Admin-Connect-EmailListener:XYZListener.Listener(com.pega.pegarules.integration.engine.internal.services.email.EmailListener)/0' failed to start because of the following error:
Failed to launch listener, com.pega.pegarules.pub.PRException: Failed to start listener: EMAIL.XYZListener.Listener From: (B084E2D2301D879AB923838EFAB7CEE89:(MBean Access))
Your sysadmin will have no idea what the error is what to do.
It would be more helpful to say, "Service could not be started, as it is using user XYZ which cannot be authenticated. Please check that the passwords match between the Service Listener record and the Operator record."