Hi There is a main office and three branch offices. The main office and two branch offices are in the same Domain (mydomain.com) but in different AD sites. One branch office resides in a sub domain (sub.mydomain.com). OWA, outbound and inbound mailflow are provided by an ht/cas server in the main office.Each office must have it own mailbox server and therefore they also needs a ht server. What about the client access server? Do I need to install a client access server in each site as well, or can I provide owa just with the cas in the main office? Thanks and regardsPeter

Yes, Exchange 2007 Mailbox server role requires at least a CAS and a HT server role in same AD site where it resides. Amit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com

Hi Peter, Please see the article below:- http://msexchangeteam.com/archive/2007/09/04/446918.aspxYou need a CAS server in every AD site that contains a mailbox server. What you could do though is use the CAS in the main office to proxy requests to the CAS in the branch offices which means that the CAS in the main office is the only one that needs to be interent facing.Hope that helps.RegardsJames

HI,Additionally Amit's post you would install at least one Global catalog server in each site where Mailbox server reside.Planning for Access to Active Directory---------------------------------------------------http://technet.microsoft.com/en-us/library/aa998561.aspxRegards Chinthaka

Thanks to all for your answers.RegardsPeter

Thanks to all for your answers.RegardsPeter Glade to hear that :)regardsChinthaka