Accessing Hosted Exchange through Terminal Services is not supported by AppRiver. If a customer wants to use the Terminal Services feature, they must clear the Use Cached Exchange Mode check box in Outlook Client. This feature does not work with Terminal Services.
Note: Since the Cached Exchange Mode feature has been disabled in Outlook Client, performance will be degraded because a local copy of the mailbox has not been retained on the terminal server. Additionally, intermittent connectivity issues may occur.
Microsoft Knowledge Base Reference: Turn on or off Cached Exchange Mode.