Problem in accessing Microsoft Outlook web app

My users are having problems trying to access their messages on Outlook Web App with the below error message. I am not sure of what to do next, whether to update my DNS settings or change E1 name server settings. Please help.

This account does not have an Outlook Web App mailbox.
You're currently signed in as [email protected]. Click here to sign out, and then sign in to your Outlook Web App account.
