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

dovecot-lmtpd is installed in your system.

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

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

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

dovecot-lmtpd package basic information: