Advanced Email Manager not filing older emails

Does anyone know if there is a limit as far as how far back the email manager will process an email? I've setup the Advanced Email Manager at a customer that's been monitoring about 5 mail boxes and creating cases. When looking at one of the mail boxes it was showing 5 unread emails from 6/10, 6/11 and 6/14. It's processing newer emails that are coming in but not these particular ones. If I forward one of the emails back to the mailbox it picks up no problem. So is there some sort of time limit it has on processing emails and why did it not process them before. They've been having to stop and start the email manager service frequently so I'm wondering if it had been down for a while and the limit is, let's say 30 minutes, then it wouldn't have processed anything older than that?? Thanks.

Brad