esmtp software package provides user configurable relay-only MTA, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install esmtp
esmtp is installed in your system.
Make ensure the esmtp package were installed using the commands given below,
$ sudo dpkg-query -l | grep esmtp *
You will get with esmtp package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | |
| Package | esmtp |
| Version | 1.2-12 |
| Description | user configurable relay-only MTA |
| Sub Section |