1: Have you tried loggingdirectly onto one fo the CAS servers and connecting to the name? I.E
https://Servername/owa What are the results? (Delete temp internet files from Interne5t explorer before testing.)
2: Is a proxy server configured in Internet Explorer when you do point one above? If so can you disable this and retest. (Delete temp internet files before test)
3: Do you get any errors logged in application event log on CAS Server?
4: Have you got SSL configured on the mailbox servers?
5: Can you post a copy of the example section of the web.config file.
<appSettings>
<add key="ConnectionCacheSize" value="100"/>
<add key="MaximumIdentityArraySize" value="100"/>
<add key="ShowDebugInformation" value="true"/>
<add key="EnableEmailReports" value="false"/>
<!-- Configurable email address of where to forward ActiveSync log messages-->
<add key="MailboxLoggingAddress" value="your email administrator"></add>
<add key="EnterpriseVault_ResourceVersion" value="v8.0.2.1693"/>
<add key="EnterpriseVault_WebDAVRequestProtocol" value="https"/>
<add key="EnterpriseVault_ExternalWebAppUrl" value="
https://mail.test.co.uk/enterprisevault"/>
<add key="EnterpriseVault_ExternalHostNames" value="mail.test.co.uk"/>
<add key="EnterpriseVault_LogEnabled" value="false"/>
</appSettings>
6: In the above on your web.config file if you change logging to be true, do yoy get a log generated in the logging folder?
7: Check out the following technotes. Some of these contain info already mentioned above, but in more detail like enabling logging.
http://support.veritas.com/docs/292348
http://support.veritas.com/docs/321015
http://support.veritas.com/docs/301813