$ sudo apt-get update
$ sudo apt-get install clamav-milter 

clamav-milter is installed in your system.

Make ensure the clamav-milter package were installed using the commands given below,

$ sudo dpkg-query -l | grep clamav-milter *

You will get with clamav-milter package name, version, architecture and description in a table

clamav-milter package basic information: