$ sudo apt-get update
$ sudo apt-get install dovecot-pop3d 

dovecot-pop3d is installed in your system.

Make ensure the dovecot-pop3d package were installed using the commands given below,

$ sudo dpkg-query -l | grep dovecot-pop3d *

You will get with dovecot-pop3d package name, version, architecture and description in a table

dovecot-pop3d package basic information: