Bug#930476: exim4 is no longer installed by default

[Alan Jenkins <alan.christopher.jenkins@gmail.com>]

Package: installation-guide
Version: 20170614

> 8.5.1. Default E-Mail Configuration
>
> [...] For this reason the packages exim4 and mutt will be installed 
by default (provided you did not unselect the “standard” task during the 
installation).

I have been told by several people, exim4 is no longer installed by 
default :-).

In Debian 9 and above, exim4-daemon-light has been downgraded from 
"Priority: standard" to "optional".

Thanks
Alan