We have a number of wireless devices (mostly Android, but possibly one or two iPhones) that connect to our corporate wireless network and note similar issues:
Non-Exchange (e.g. Gmail, Hotmail) accounts do not automatically sync while connected to the corporate wifi network
Some devices allow for manual sync while others won't sync at all
Sync works properly when on 3G/4G networks and when on other wifi networks
After taking one device, assigning it a static IP, and opening it up entirely through the firewall, autosync does seem to work (albeit perhaps a bit slowly?)
All mail services are accessible through their respective web interfaces
This all suggests to me that it's a simple port issue in the firewall, but I can't find information on which specific ports need to be opened. Any thoughts? Thanks in advance!