Cisco :: Connecting Back To Network Through External Interface?

I have a ASA 5505 configured with three VLANs: Inside, Outside, and DMZ.I am running an exchange server on the Inside network and have configured NAT to allow connections to it from outside. This works fine. I can also happily connect to it using it's internal address from the inside. In the DMZ I have setup a linksys router to work as a guest wifi network. I configured the ASA to block any traffic from the DMZ to the internal network.This has been working fine for the last few weeks.Wireless users cannot access any internal resoureces, but can browse the internet etc.. etc..

My problem is that I want users to be able to connect to the wireless with smartphones, tablets etc..., if they do so, they can access the internet, but not get their email. From my (limited) understanding, the problem is that the ip address I am trying to connect to is the same ip that I am transmitting from. Is there any way to send the packets to the outside network and then loop them back to the exchange server?