Outlook won't connect if no default gateway on NIC

Outlook won't connect to the Exchange server if you don't have a default gateway on your network card. Why would you have this problem? I didn't have a default gateway because I was temporarily using the PC as dual homed (two network cards). I wanted the default gateway to be set on one card and not the other. Then I repurposed the machine without checking and using the NIC that didn't have the gateway. Outlook balked, and I panicked a slight bit. How is it possible that I have every network (Internet, files, database, etc.) and no Exchange connectivity? Especially since my other box is chugging away perfectly on Exchange. Exchange error messages actually said this, and sure enough, it was correct.