I'm running Exim 3 under Debian, and want to upgrade to Exim 4. How difficult is it?

There is an article covering this issue on Debian Administration http://www.debian-administration.org/articles/98

A user who did this, using the Debian Exim 4 package, reported as follows:

1. The exim4 package installs easily, and the exim (3.38) package stalls at the same time.

2. Exim runs from inetd. Exim4 runs from /etc/init.d. Much nicer!

3. The exim configuration file is found in /etc/exim/exim.conf. The exim4 configuration file in /var/lib/exim4/config.autogenerated. It is, as the name suggests, autogenerated.

4. A new directory is created called /etc/exim4. This contains the files to generate the above config. You make changes here.

5. Once you have made changes to the files in /etc/exim4 you run update-exim4.conf which generates a replacement.

[Debian maintainer: You also need to tell the Exim daemon to reread the changed configuration. You can do this using SIGHUP by hand. Alternatively, instead of running update-exim4.conf you can use

invoke-rc.d exim4 reload

which does the rebuild and also tells Exim to reread the changed configuration.]

1. In my experience, you need to carefully check the generated config files. For example, it did not generate a system filter file reference in the nfig.autogenerated.

2. All of this may be in the docs. I've read some of them, obviously, didn't come across an actual upgrade guide.

[The Debian maintainer says: /usr/share/doc/exim4-base/README.Debian.gz and update-exim4.conf(8) should answer most of the questions.]