OWA 2010 and 2013 coexistence

Hi,

We are migrating from Exchange 2010 to Exchange 2013. We use Enterprise Vault 11.0.1 Cumulative Hotfix 2 to archive Exchange 2010 mailboxes.

All our clients from internal and external access use OWA.

Using Internet Explorer we navigate to CAS 2013 URL. And try to login with a 2010 mailbox. CAS 2013 proxies to CAS 2010 and Vault doesn't works. Today we found this article: https://www.veritas.com/support/en_US/article.000020535

We gonna change our internal DNS to use  https://mail.domain.com/owa and point it to CAS 2013. But if users with mailboxes in Exchange 2010 can't use Vault, we can't migrate. And use differents URL for 2010 and 2013 mailboxes is not an option. We need to use https://mail.domain.com/owa for all mailboxes.

How can we resolv it? Anybody knows a similar problem in their enterprise?

Regards