We've recently configured a new Server 2012 with exchange 2013. Everything seems to have gone well.

For some reason, We are unable to connect to the exchange server from a clients PC using the exchange option however, if we choose activeSync then we are able to access the mail. What is the difference between activeSync and Exchange option in outlook and what could be causing the issue?

I've already checked the DNS and the client machine is connected to the domain. The owa can be used successfully on the clients PC. I've tried everything I can think of to debug the issue and I think it will be something stupid that I have forgotten to do to enable this. Has anyone got any suggestions as to what this may be?

I will note however that there is no internet at all and this is just through an internal network that has been configured. So the emails I have tested have been to local email addresses.

Also, the error that I am recieving when I connect from outlook via exchange option is:
The action cannot be completed. The connection to microsoft exchange is unavailable. Outlook must be online or connected to complete this action.

• Edited by LSorsby Monday, August 03, 2015 1:11 PM Added more information

Make sure that the RPC ports opened between your CAS servers and your active directory in case you have them in separate VLAN and you Configure static RPC ports on your Exchange client access servers.