$ sudo apt-get update
$ sudo apt-get install gosa-plugin-mailaddress 

gosa-plugin-mailaddress is installed in your system.

Make ensure the gosa-plugin-mailaddress package were installed using the commands given below,

$ sudo dpkg-query -l | grep gosa-plugin-mailaddress *

You will get with gosa-plugin-mailaddress package name, version, architecture and description in a table

gosa-plugin-mailaddress package basic information: