Hi, I wonder if anyone can help advise or point me in the right direction. We have two AD sites one in the UK and one in the US with Exchange 2010 servers in each. Only the UK site has an ISA server which is publishing OWA externally using Forms Based Authentication with RSA SecureID. If a user is based on the UK Exchange servers then external access works perfectly and OWA load up normally. When a user in the US tries to login OWA attempts redirection which fails to work as the URL internally is not available externally. External URL: mail.blahblah.com Internal URLs: uk-mail.blahblah.local and us-mail.blahblah.local On both the UK and US CAS servers I have configured an additional IIS site with OWA and ECP using Basic & Integrated authentication for use with ISA (lets call this site IIS-Ext). ISA authenticates the RSASecureID and then passes the Windows Credentials onto the IIS-Ext for the AD authentication. On the UK IIS-Ext CAS servers I have configured an External URL but the US IIS-Ext CAS I have left them blank. On the UK IIS-Ext CAS I have configured 'RedirectToOptimalOWAServer' = $false. I am still having no luck. Any suggestions? Many thanks in advance. Bara