Small Business Server 2008 without Exchange… how and why

I'm fairly confident the problem was one of or a combination of:

1. Setting a Secondary DNS server from my ISP rather than leaving the SBS server as its own sole DNS server.
2. Disabling IPv6 because I believed I didn't need it.

I've since reinstalled and avoided disabling IPv6 or setting a secondary DNS server (instead adding our ISP's DNS servers as forwarders in Admininstrative Tools → DNS Server). I've yet to see any issues, although that's not to say they won't return.

However, if anybody can explain in an answer how exactly one or both of these would have caused my issues I will gladly give them the accepted answer.

The only real reason you'll need to use Windows Server 2008 R2 Enterprise edition for Exchange is if you want to use the high availability DAG features of Exchange 2010.

The requirement of the Enterprise edition of the operating system is because DAGs use pieces of Windows clustering to do their thing, which is not available in the Standard edition.