What the hell is Microsoft doing with the SMTP service? They still have it running in the IIS 6 manager even on Windows Server 2008 R2 and every few months they keep releasing updates which reset the configuration/settings breaking the service.
This is the third time a Windows Update has done this to me this year. It either entirely clears all of the settings for the SMTP service or just things like the "fully qualified domain name" back to the host's name.
A quick google will indicate that this is both common and has been going on since at least 2010. You can find a whole list of Windows Update which are causing the service to lose its configuration information.
Unfortunately as Microsoft has no channels of direct communication posting on C9 is my only option.