Recently Outlook began prompting users to enter their credentials. The strange thing is, the logon box's title indicates it is attempting to connect to our outside FQDN instead of the internal one (remote.domain.com).
This is a very common question in the last month for SBS 2008 users. It is resolved by approving rollup 9 for Exchange 2007 in Updates.
Another option would be to install Exchange 2007 Sp2 as the wrapper for installation on SBS 2008 is now available.