Let me know what Term you are using for the WEBMAIL USER?? Lets talk on the correct issue and not try to twist or waste time. Please check the details and screenshot below for your better understanding of the concern all Webmail users are facing...
And most importantly HOW the webmail user change the "PASSWORD" Themselves from the Webmail which is available since ages for other control panels like cPAnel / DirectAdmin/ Plesk etc.