So after the last change, you entered your email password and it works until the next change? Or, is it more frequently than just one time after the windows password is changed every 90 days?

It may be part of a script they have set up to run when it asks you to reset your windows password, can you ask your IT if this is the case before you try anything else? We really don't want to go further if they have it set this way for a reason. They might want to try the steps below if they don't have a script that reprompts for you email authentication (kind of like what you thought earlier).

If not:
If Outlook asks you to enter your password every time you check mail although you have Remember password set for the account, wrong settings for the "Protected Storage System Provider" might be the cause. Read through this whole article and make sure you understand it before making any changes to registry as it eventually suggests.

http://email.about.com/gi/o.htm?zi=1....com/kb/290684