[otrs] Bounce emails without ticket numbers

How do I have the system bounce emails that do not contain ticket numbers? When ever I enable this option in sysconfig the POP3PostMaster.pl PID always hangs and I get the following error: [Notice][Kernel::System::PID::PIDCreate] Can't create PID PostMasterPOP3, because it's already running yourhost.example.com/1837)!