Troubleshooter: Conflicting Logon Credentials Prevent Migration

My company has several users who run Outlook Express against a UNIX IMAP server. We want to migrate those users to Exchange 2000 Server. However, their logon credentials don't work. We receive the error message BAD Protocol error: Provided username is not valid. Do you know what the problem might be?

This error message typically occurs when an IMAP client uses the Fully Qualified Domain Name (FQDN) of the IMAP server. Most UNIX IMAP servers expect you to log on following the format username@fqdn (e.g., [email protected]). However, Exchange 2000 accepts logons that include the NetBIOS domain name, not the FQDN of the DNS domain in which the server resides. If you specify only the username (and no domain) in your users' Outlook Express settings, the users should be able to authenticate properly.