Can SquirrelMail be used to change the users' passwords?
As you probably know, SquirrelMail doesn't store any passwords. It's the IMAP server's responsibility to take care of this, and it can choose from a number of different backends, such as SQL or LDAP database for instance, to perform this task. Fortunately, there are several SquirrelMail plugins that, depending on how your system is set up, can be used as a change password interface.
It you're using SquirrelMail 1.5, try the included change_password plugin first. If it doesn't work, or if you're running some other SquirrelMail version, try the plugins at the [change password] plugin page.