I have Server 2008 with Exchange 2007 all running fine inside the office and for external users (new TS portal is GREAT!). However, when laptops (both Vista Business & XP Pro) that are on the domain are outside the office, hence off-line, they get a message along the lines of "Cannot access the Exchange Sever at present". The users can create MESSAGES that will sit in the Outbox until connected but this problems just applies to off-line Calendar entries. They connect via RCP over HTTPS all fine, with auto-detect doing it's stuff.
NOTE: However, if I set up outlook on a PC outside the office that hasn't been added to the domain I get no problem adding an appointment if off-line!
The correct sync boxes are ticket for Outlook just in case you're wondering!
Look forward to your suggestions...