IADT password expires every 90 days. Users are given notice from 14 days prior to it expiring on Microsoft OS based computer. When you change your password you cannot use your last 10 passwords.
If you access your email remotely or internally from a Mac or Linux through the web and your password is with-in 14 days of expiring you will get a similar message.
The below document will guide you through how you change your password through the Web.
A Guide To Changing Your IADT Password Online (pdf , 267 kbs)