MS Outlook and OWA doesn't connect behind Untangle

Dear All,

I am new to Untangle so need help. I installed Untangle to monitor traffic and allow/block websites. Everything works fine but my MS Outlook client and OWA doesn't connect when they are behind Untangle.

We have a small office setup, a hardware firewall, couple of domain controllers and MS Exchange 2010 hub+cas servers inside.

Present Connectivity:
- Exisiting firewall's external port is connected to ISP.
- Internal port is connected to a small switch, which is further connected to a switch array that provides connectivity to client computers.
- This small switch has all servers (domain controllers, Hub+Cas, DNS, DHCP) connected to it as well.
- I have configured Untangle in bridge mode. Everything works fine (like webfiltering etc) behind it except MS Outlook and OWA (they don't connect)
- I even tried switching off Apps/options in Untangle but the situation remains same.

I will highly appreciate help in this regard.

Best regards,
Aamir