Can i use same certificate on 2 different CAS Server across sites

Question

Hi All
I have a question I have been playing with for a few days,
I have the following setup,
2 sites connected via a VPN and a DAG configured between sites.
Site 1-Head Office
2 exchange 2010 servers,
1 running CAS and Mailbox (this server is entry point to all clients for owa etc.)
1 running Hub, CAS, Mailbox. (this is the main server and a DAG Member)
We have a UNC certificate associated with all records pointing to remote access and its installed on both servers.
** Everything in this site works fine.
** The AD DNS server does not have a zone for the public domain with all the external records only the .local domain. Planning to change this soon.
Site 2.
1 exchange 2010 servers,
1 running Hub, CAS, Mailbox. (this is the main server for this site, a DAG Member and no entry point at this time but we intend to use it for redundancy)
** Currently all BD are on server in site 1.
** The AD DNS server does not have a zone for the public domain with all the external records only the .local domain. Planning to change this soon.
My questions are as follows:
1      on site 2’s the cas server can I use the same certificate I’m using onsite 1. in other words all clients currently use mail.domain.com which has an IP pointing to site 1, can I use that same certificate in site 2 and associate
it with the CAS server there? (in the event of a failover I just change the records IP)
2      All smtp traffic come through site 1, when I test moving active databases to site 2, all email stay in the ques of exchange server in site one, they don’t get delivered. (I have not set AD replication through smtp so don’t know
if this is a factor)
3      When I do set the active databases to site 2, webmail and remote services stop working, I get the infamous error when logging onto webmail, service unavailable because it’s been moved. I have read a lot about this being an internal
external url issue.
All these issues im starting to think they all interlinked, and would like some help.
Cheers

Answer 1

Answers to your questions:
Yes.  Understand that until you swap your external DNS so it points to Site 2, the mail.domain.com won't be accessed, but it will be there for when you want it to be.
AD replication is not the issue, so don't try to set it to use SMTP.  If you have hub servers in both sites, your inbound Internet email should be delivered from the Site 1 hubs to the Site 2 hubs.  We may need more information before we can give
you a good answer for this question.  However, you may check the following TechNet article (and its links) for assistance. 
http://technet.microsoft.com/en-us/library/aa998825(v=exchg.141).aspx
Web access requires that the CAS you connect to be either externally accessible and in the same site as your mailbox server, or that the CAS in the inaccessible Windows site needs to be configured as internal only and the accessible CAS needs to be configured
to proxy connections.  For this, make sure you have followed the directions in the following TechNet article.
http://technet.microsoft.com/en-us/library/bb310763(v=exchg.141).aspx
HTH ...