it could be your system has troubles processing. That for some reason mails piled up, and now the system isn't fast enough to manage all the mails.
I had something similar. I shut down the smartermail service. moved all mail in de spool folder to a new location. Started the smartermail service, and copied the mail back in batches (.eml + .hdr in pairs) to the working spool directory.

Thanks Richard, but I am working with SmarterTrack and I don't see a service to stop. I was thinking about doing basically the same thing and then restarting the server and moving emails slowly over. That should do the same thing...I think.

Hello,

I'd recommend submitting a ticket. We can take a closer look and solve it for you. 

Regards,