Accesing Mailbox via OWA on DR Server

Hi,

I am not 100% sure if this is possible so I will give a summary of how our site is setup.

We have 3 exchange servers, two onsite and on at a DR site

EX1 - Exchange Server One - Onsite Head Office
EX2 - Exchange Server Two - Onsite Head Office
EX3 - Exchange Server Three - Remote DR Site

Our servers are setup in a CAS array with mailboxes split 50-50 between EX1 and EX2 and accessible from via OWA by going tohttps://owa.domain.com/owa

There are no active mailboxes on the DR site, it is there for failover purposes and mailboxes only become active if EX1 and EX2 fall over.

As we are a global company what we would like to do is setup an externally available OWA site on EX3 (https://dr.domain.com/owa) so if we have a major line outage at our Head Office then we can tell our satellite offices to connect to their mailbox on the DR OWA site.

I create the A record for this and configured the certificate etc and I can access the OWA page fine, however when I logged in to my mailbox (on EX1) with my details I got a message stating..."Use the following link to open this mailbox with optimal performance: https://owa.domain.com/owa" - this is obviously because my mailbox is on another server.

I found a command that I can run "set-owavirtualdirectory “owa (default web site)” -RedirectToOptimalOWAServer $false"which would mean the site would not automatically try and login and I ran the command however when I log in the URL redirects tohttps://ex1.domain.local/owa/ping.owa which is the local address and I get a blank page. I can remove the ping.owa at the end and it will take me to my mailbox. However that doesn't really help because if we have a line outage it won't be able to access EX1.

My question is, is it possible to access my mailbox from EX3 (our DR site) without the mailbox database being mounted on that server (the database is listed as healthy as it will only failover if the first two servers experience problems). Essentially all we want to do is create a secondary website (which I created above) that points to our DR site in case we have an internet outage so any of our satellite offices can still easily access their mailboxes whilst we fix the problem.

If anybody requires any more information please let me know.

Thanks in advance.

David