Change the URL for OWA displayed in Outlook

Hi,

I have an Exchange 2010 system with 2 CAS-HUB server + 2 Mailbox server.

I have 3 owa virtual directories for 3 sub-companies in my organization. For example:mail.abc.com; mail.def.com, mail.xyz.com. All accounts in one domain.

Outlook 2010/2013 displays one of these URL for "Access this account from the web". For example:mail.xyz.com

Now I want to change the URL displayed by Outlook into another OWA I have, for example:mail.abc.com, but cannot find any information.

Please give me an advice.

Thanks,