Hello,
I am Prosenjit an expert in AWS, Azure, VMware and multiple Microsoft technologies.
This is a place holder bid to start the discussion and understand your issue. In the project description, you didn't mention the email server you are using. Hence. please let me know if you are using Exchange Server or some other email solution. I am not worries about Windows Server version as I have worked on Windows NT Server to Server 2016.
Best regards,
Prosenjit SEN