Your .NET framework will need to be updated, and .NET 4.7 installed at the very least. Your IIS version should facilitate set up of SmarterMail, but may also require updates (Windows Updates.) You can operate SM (latest) on Server 2008 but we cannot recommend or support this configuration as it lacks some key functionality we require to operate smoothly. My suggestion in this case would be to ensure you're running the latest available minor release of the version you are on currently (i'm assuming SM v15?), and then plan for an upgrade to SmarterMail (latest) once the server upgrade becomes feasible.