[exim] Please Help with performance tuning

Hi,

I'm new to Exim, I've been using it for a short time and have been reading
up on how it works.

I have a Debian linux server running Exim, and another server running
mailman is using the Exim server as a relay, so all deliveries to the list
are done through Exim.

I have a large list in mailman, with SMTP_MAX_RCPTS set to 10 and I see in
the Exim log all of the incoming messages for the list:

grep -c "<= list-bounces" exim_stage1/mainlog |more
4361

So basically I see there are 4361 queue entries for the list, (only 1
message sent to the list).

Now, many hours later, I would expect a significant number of deliveries.
I have Exim logging to show the F= to make it easier to track down. But
I'm very surprised to see that there are only a very few messages actually
processed for delivery.

grep -c "F=<reflexoes-bounces" exim_stage1/mainlog
1344

(I know this includes both successful deliveries as well as any temporary
or permanent failures -- the point here is that after 8 hours, 1344
messages processed is way too little)

Now taking the last couple successful deliveries as an example, here's
what I see:

2009-08-08 21:37:43 1MZssc-0002HX-7E => melnicky@???
F=<list-bounces@???> R=dnslookup T=remote_smtp
H=vip-us-br-mx.terra.com [208.84.244.133] C="250 2.0.0 Ok: queued as
359AB700000E1" QT=7h46m37s DT=1s
2009-08-08 21:37:45 1MZssc-0002HX-7E => olivatto@???
F=<list-bounces@???> R=dnslookup T=remote_smtp
H=howard.atarde.com.br [187.1.111.123] C="250 Ok: queued as 82EAA3F94B4"
QT=7h46m39s DT=3s

both these deliveries spent almost 8 full hours in the queue!

The incoming queue right now still has over 4600 entries waiting to be
flushed out or completed.

What am I doing wrong, how can Exim be configured so at least it can
process all of the incoming queue entries in a timely fashion?

Also the server is not loaded at all, it's quite idle.

# w
21:40:51 up 9 days, 7:10, 1 user, load average: 0.78, 0.38, 0.20

In my previous setup this large list would be delivered in just a couple
of hours. With my Exim setup, after 8, it's barely making a dent.

Thanks for any help.

Ricardo