AfterLogic Webmail Pro password change plugin for postfixadmin
Simply put the files into a directory postfixadmin-change-password inside your data/plugins folder.
And set the following config directives in data/settings/config.php:
'plugins.postfixadmin-change-password' => true,
You should be good to go!
Based on plugins.poppassd-change-password plugin by AfterLogic.