Optimizing exim performance

Hi,

Recently, I experienced that exim was slow in sending outgoing mail, it was spending a lot of time in the queue, resulting in customer complains.

I came across an article in the internet to optimize the performance of exim in the server. However, the location of the exim.conf is not in /etc/exim.conf in my server. It is /etc/exim4/update-exim4.conf.conf. I just want to confirm if this is the correct file to make the configuration changes to?

Also, one of the steps given to optimize the performance is to :

However there is no /etc/init.d/exim in my server, only /etc/init.d/exim4. I assume this is the correct file to edit, however, I do not find the keyword "QUEUE" in it. How do I edit this file for this option? I only see this two variables that I think are somehow related:

QUEUERUNNER='combined'
QUEUEINTERVAL='30m'