[Dovecot] How can I add change_password

Hello I use dovecot, postfix, mysql and squirrelmail as a mail server. it works well. Meanwhile I am novice at postfix. As you know, there is a change_password plugin on squirrelmail. I wish to add change_password plugin on squirrelmail. I couldn't find how to integrate postfix and change_password. How can I add it ?