I have two AD sites, HQ and DR, with separate IP subnets, linked over site-to-site VPN.  Each site has a DC with DNS server.

I have a multi-role Exchange Server 2013 box.  When I move it from HQ to DR, making correct IP address change with local DNS server, connection to mailboxes using OWA or Microsoft Outlook does not work.  Issue was CAS server.

Resolution I found was to change the AutoDiscoverSiteScope attribute for the ClientAccessServer schema setting so it is authoritative for both sites:

Check AutoDiscoverSiteScope and set for both sites

Get-ClientAccessServer | ft name,AutoDiscoverSiteScope

Name                     AutodDiscoverSiteScope
----                     ----------------------
SRV-EXC                  {Site1}


Set-ClientAccessServer SRV-EXC -AutoDiscoverSiteScope Site1,Site2


Get-ClientAccessServer | ft name,AutoDiscoverSiteScope

Name                     AutodDiscoverSiteScope
----                     ----------------------
SRV-EXC                  {Site1, Site2}

Hi,

Thank you for your sharing.

The AutoDiscoverSiteScope parameter specifies the site for which the Autodiscover service is authoritative. This attribute is set when the cas server was installed, and it never changed automatically, manually changing is neccessary when move cas servers between sites. Besides, we can configure Autodiscover service to Use Site Affinity.

Here's an blog about it, for your reference: http://blogs.msdn.com/b/brad_hughes/archive/2007/09/11/autodiscoversitescope-and-client-only-sites.aspx