outlook 2010 owa error

[AbsyntH]

hi
i'm tring to connect outlook 2010 using owa capability but it returns this error when it tries to check username at the end of the account's creation " The action cannot be completed. The Connection to Microsoft Exchange is unavailable. outlook must be online or connected to complete this action."

my config is:
zentyal 3.5.2

eth0 internal ip 192.168.1.42
eth1 external ip 192.168.2.2 ( i've only one public ip addr...so i can't use it on the external Interface)

dns module
hostname kthulu , ip address 1.42 , alias autodiscover
hostname remote , ip address 2.2 AND $MYINTERNETIPADD , alias autodiscover

firewall nat 443 and 80 against the eth1

rpc on openchange

Host name remote.mydomain.it (it's correctly resolved by google dns )

i've followed 
https://wiki.zentyal.org/wiki/En/3.5/OpenChange_%28Microsoft%28R%29_Exchange_native_replacement%29#Configuring_the_Microsoft.C2.AE_Outlook_Client