1. Download the dependencies through composer and then start manual installation. (since 4.0.1)
2. set $CONF['configured'] = true; and also enter the database details in config.inc.php file in manual installation
3. PHP REQUIREMENT LINK : requirement display on setup page of installation (check composer.json as well). \vendor\composer\platform_check.php
4. Release date : https://github.com/postfixadmin/postfixadmin/releases/