Outlook 2010 exchange setup prompts for [email protected] rather than [email protected]

We use a hosted exchange service.

When users want to set up Outlook 2010 to access their account, they open Outlook and run through the configuration steps.

Autodiscover is enabled, and in the user's active directory profile, their email address is in the email field.

However, when the configuration process reaches a point where they are prompted for their email account's username and password, their active directory username is filled in by default instead of their email address. Is there a way to fix that?

Users get confused and try to enter their email password over and over again and wonder why it doesn't work (and completely miss/ignore the "use another account" button even though they have instructions right in front of them).

I'm also using the Office 2010 ADM's in group policy, but I haven't yet seen an option to specify what gets auto-populated in that windows security prompt.