$ sudo apt-get update
$ sudo apt-get install exim4-daemon-heavy 

exim4-daemon-heavy is installed in your system.

Make ensure the exim4-daemon-heavy package were installed using the commands given below,

$ sudo dpkg-query -l | grep exim4-daemon-heavy *

You will get with exim4-daemon-heavy package name, version, architecture and description in a table

exim4-daemon-heavy package basic information: