We have an SBS 2011 server running Exchange 2010 SP3 and two domain-joined Terminal Servers running Outlook 2010 & 2013.
When any Exchange account is configured to Connect to Microsoft Exchange using HTTP (the default for all users) Outlook prompts for a username and password. Everything works when you provide valid credentials. If Connect to Microsoft Exchange using HTTP is turned off Outlook connects without prompting for credentials.
Also, Outlook Anywhere does not work outside of our local network. Outlook Web Access (OWA) works fine from inside and outside the network. We have also confirmed RPC Client access is working.
I have a feeling there is an issue in IIS, but I'm not sure.
Our orginisation is a too large to go to each user and turn off Connect to Microsoft Exchange using HTTP.
Does does anyone have any ideas?