How Can I Change an Email Account Password Without Using the Postmaster Account?

Any email account can be used to login to Qmailadmin (http://mail.highspeedrails.com/cgi-bin/qmailadmin). Instead of using postmaster as the username, use the handle (part before the @) of the email account and that email account's password. The owner of that email account will be able to login and manage his email account alone, including changing his/her password or setting a vacation message.