This App is for using with postfixadmin. There's no possibility to change a mailbox-password without being administrator for a domain. The first goal of this app is to login with a mailbox and the current password and to change the password afterwards.
Please have a look at the wiki to see installation- and further instruction.
You're using this app on your own risk. I've tested it and it should work, but I still can't take any responsibility for data loss or any other damages. Everyone is free to use and modify this app as long as you publish it on the same conditions (like free to everybody).