[CentOS] Postfix smtp freezing

Hey all,

For the last 8 months I have been running a postfix / mail scanner setup 
based on Johnny Hughes' excellent tutorial.
For the firs 7 months I have had no issues. This past month I have been 
having instances where the user gets an smtp error while trying to send 
email.
Restarting the postfix service is all it takes to resolve this issue. 
The problem is that it has begun to occur more and more often. It is now 
up to once every day.
I have found nothing unusual in the mail or messages logs. As I am an 
ultra newbie I am unsure of the next step to take to resolve this.
I have search through the past messages on this list and can find 
nothing. Anyone have any ideas?

Thanks,

Jason Ross