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

dovecot-imapd is installed in your system.

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

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

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

dovecot-imapd package basic information: