Difference between exim.conf and config.autogenerated

I executed dpkg-reconfigure exim4-config and it generated /var/lib/exim4/config.autogenerated. I believe that this is the master configuration. However on our older server with an older version of Exim I have seen exim.conf in the /etc folder. What is the purpose of this file and how can I generate it? Is there a tool that can generate it and is it recommended to have this file?