[exim] Performance question :-

I'm having a little trouble with performance on one of our email servers :-

Spec :-
HP DL380 Dual 2.4Ghz Processor
4GB Ram
3*36GB 15K RPM Disks in a Raid 5 (64MB read cache)
RedHat Enterprise 3 Linux
Exim 4.41 With exiscan & SpamAsassin compiled in.
Split Spool directories
Exim spool directories are on a seperate filesystem though the raid is configured as a single disk.

Throughput constant 7000 messages per hour ( ~116 / min)

The system is not CPU bound ~25% cpu usage as an average, neither is it memory bound. It has 1.6GB Ram free with none of the swap used.

The system takes in an email, uses LDAP to authenticate the user then delivers it via 2 routers to 2 seperate destinations (one is an archive server) the other is a content/virus filtering system. Then the message is passed back to me for final delivery. (The above count of 7000 / hour includes the message the 2nd time round.)

The issue I have is that between sending the "." at the end of the data and receiving the 250 message with the spool ID there can be anything from 5 to 30 seconds delay.

The spool queue is ~88MB with around 2500 messages in the queue at any one time - bounces defered deliveries etc.

Obviously the system is IO-Bound, I was wondering if there was any advice on how I could reduce this delay.

Thanks..

-Andy-