I have a really interesting approach for you...

Make a report that has the query that would capture these stuck inbound records... say for the timeframe of last 2 hours...  Then make a scheduled job that will email whoever if the report runs and it finds record- then check OMIT if not records- so you have a cool process that will run the report every x hours and alert you if any records come up. Now the better thing is to find the root cause here- perhaps these records are treated as spam and ignored- perhaps certain ones really should be... like for emails from a locked account spamming the system..