$ sudo apt-get update
$ sudo apt-get install kgmailnotifier 

kgmailnotifier is installed in your system.

Make ensure the kgmailnotifier package were installed using the commands given below,

$ sudo dpkg-query -l | grep kgmailnotifier *

You will get with kgmailnotifier package name, version, architecture and description in a table

kgmailnotifier package basic information: