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

dovecot-ldap is installed in your system.

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

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

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

dovecot-ldap package basic information: