The following message appears during SMEX 11.0 installation running on Windows Server 2012 or Windows Server 2012 R2:
.Net Framework 3.5 SP1 must be installed before to setup ScanMail
The error occurs because the two security updates 2966827 and 2966828 prevent the optional Microsoft .NET Framework 3.5 from being enabled.
To solve the error, you should remove the two security updates. You may follow the procedure on the Microsoft article: Update for the .NET Framework 3.5 on Windows 8, Windows 8.1, Windows Server 2012, and Windows Server 2012 R2. In return, SMEX 11.0 can be installed.