CAS 2010 to CAS2007 silent redirection is not working

I am doing migration from Exchange 2007(SP3) to Exchange 2010 (SP2). I am getting the below message while CAS redirection. It's redirected to exchange 2007 mailbox once I clicked on legacy.domain.com. 

Use the following link to open this mailbox with the best performance.

https://legacy.domain.com/owa

I have set the OWA virtual directory for silent redirection. I was wondering why it's not redirecting silently and asking to click on legacy link.

Any ideas??

Thanks,

Nitin

Nitin