ip firewall nat - port forward (even with internal request)

so I have a network where smartphones access an internal exchange server and when they come on site and their wifi picks up, they’re now on the corporate subnet. the port forward stops working to the exchange server unless they disable the wifi and use the cell networks.

i have this:

chain=dstnat action=dst-nat to-addresses=10.0.0.10 to-ports=443 protocol=tcp dst-address=8.8.8.8 dst-port=443

the traffic gets to the server no problem but i’m failing to comprehend why it isn’t getting back to the src-address on the local subnet.

any help would be appreciated!

http://wiki.mikrotik.com/wiki/Hairpin_NAT