Hello Philip, the last version of SmarterMail that is recommended for use on Windows Server 2008 is SmarterMail v15. SM v16 and our latest both require SignalR (WebSockets) and .NET 4.7.2 for proper functionality.
Once logged in to your
SmarterTools.com account you can access the
Legacy Builds section from the menu at the top right-hand corner of the page.
Kyle Kerst
IT Coordinator
SmarterTools Inc.
www.smartertools.com