My company is growing a lot the last couple years. Globally, I have offices in Romania, Spain, Vietnam, China, Singapore plus couple other small offices. We currently have 2 CAS/HUB Servers (VM) and 2 Mailbox Servers in a DAG (physical) installed in the US. In order to improve the performance to our users in different part of the world, I am planning for diversifications. So I am planning to deploy 2 CAS/HUb and 1 Mailbox server to Bucharest, Romania to take care of Europe and 2 CAS/HUB and 1 Mailbox server to Saigon, Vietnam to take care of Asia. My ping rate to Romania is 180ms and to Vietnam is 173ms over Sprint MPLS cloud. Since I have 2 Mailbox servers(in a DAG) in the US, I would like to hold the passive copy of databases of Vietnam and Romania in the existing two US servers. The Mailbox servers in Romania and Vietnam will be holding their own Active Copy of databases. Do I run into site issue with Mailboxes in different locations? If one mailbox server went down, how do the local cas server talk to the mailbox server located in the US? How do I configure the local cas servers for the local users in that country to access their email? I am thinking another domain name in the internet such as romania_cas.mycompany.com and vietnam_cas.mycompany.com. I heard something like affinity can take care of the CAS issue but not sure. If so, anyone can give me an example of how to configure affinity so that I only have to keep one URL for all my users? Thanks.

Thanks Sergey for your answers. Can you clarify what do you mean by "add regional domain for each site"? Can you give an example? I do have site configured in my AD. Yes, I do want to use Outlook Web App and Outlook Anywhere? Do you recommend using differern URL for each site or use One URL for the whole corporation? What are the advantages and disadvantages? Thanks.

Thanks a lot for your direction. Take care!