We have recently started deploying servers at a second datacenter, and deployed a standalone array of TMG servers as a web proxy. The servers have no access to the internet without going through the TMG array. So far everything is working except Outlook connecting to exchange, which is at another datacenter (behind another forefront TMG array). Outlook is using the default RPC over HTTPS. It's the exact same issue/errors as this thread (http://social.technet.microsoft.com/Forums/forefront/en-US/39a9cf10-7b68-47bf-8c3c-ea9af5f5564c/create-rule-to-allowed-outlook-clients-to-access-an-external-exchange-server?forum=Forefrontedgegeneral), but there was no resolution there.
When setting up the email account, everything works fine. But when you try and start outlook, it fails to open saying it can't connect to exchange. A repair on the connection through control panel -> mail works, but outlook still fails to open.
I have tried the following to get the issue resolve:
1- Created an outbound allow all rule for testing purposes. Nothing is being blocked, but the connection still fails
2- I have tried without the TMG client installed, and with the client installed. Both failed.
3- I have tried multiple times with different profiles on different servers. They all failed the same way.
4- I have looked through this link, but it's for ISA 2004/Outlook 2003, so I can't find any of those settings in TMG 2010 (http://www.isaserver.org/articles-tutorials/articles/2004olpop3smtp.html)
