Unable to get connected to Exchange Server through IMAP4 using domain\username format , from Groupwise client

Using GroupWise client to connect to Exchange Server via IMAP 4
The Exchange Server is servicing multiple domains
Need to use Domain/Username format as the authentication credentials on the GroupWise client , while creating an IMAP account
Getting error "Logon Failure : Invalid User Strings"
Works fine when simple user name or username@domainname is used in the user credentials , while creating the IMAP account

This is working as designed . GroupWise client does not support "Domain\Username" format.
Need to configure the Exchange server , to accept simple username or username@domainname for authentication.
Use other Third Party Email Clients like "Thunderbird" or "Evolution".