[exim] Speeding Up Exim

> I just got a call from someone wanting to be able to send 50k email
> messages a second. Most of it in bursts of a few seconds long. It has to
> do with some kind of gaming application. I'm just trying to picture in
> my mind what kind of hardware could do that.

I have an Directadmin based email/web server. Its based on CentOS
32bit 4.4, Exim, Dovecot, Spamassassin-3.2.4, Clamav and etc. Maildir
based.

Hardware is:
AMD64 Dualcore 3800+ just updated to 5600+
4Gbyte DDR2
SATA2 500GB drive

Normally load average is like 8 or less but at peak times I am seeing
it spike to like 100 area. Upgrading the CPU gained very little. I
am thinking I am disk I/O bottle necked. I have about 2000 email
accounts and according to eximstats at peak times I am seeing
"Messages received per hour" of 40K.

I have added a few scripts hoping they would help. I now auto suspend
email accounts that have not been checked in 6 months. Few other
scripts for cleaning out old high scoring spam from mailboxes
infrequently checked. Also bounce based on a few blacklists at MTA
time. Cannot be too aggressive there else users complain.
Spamassassin does a very good job. Very rarely does a false positive
but does let some SPAM slip by.

Any other ideas to speed it up at peak times? Hopefully without
starting from scratch with crud load of downtime.

I wander if the SATA feature of NCQ would speed the disk I/O up but
there is likely no easy way to upgrade CentOS 4.x to do that.

Matt