Note: Microsoft Windows Server 2008 is no longer supported as of WorkflowGen version 7.11.0. We recommend migrating to Windows Server 2012 or later.
Even if this feature is deprecated, SMTP Virtual Server is still available on Windows 2012 features. “SMTP and the associated management tools are deprecated. Though the functionality is still available in Windows Server 2012”
For the current version of WorkflowGen, you have to install this feature as Windows 2008.