With the release of the following Exchange updates Microsoft has announced TLS 1.2 can be strictly enabled on the Exchange server and older TLS/SSL versions can now be disabled.
After disabling TLS 1.0 and TLS 1.1 on the system Symantec Email Submission Client (SESC) no longer seems to be functioning.
Symantec Email Submission Client (SESC) was compiled using .NET 2.0. The prerequisites for installation of SESC indicate .NET 3.5 is required due to the inclusion of .NET 2.0 for Server 2008R2 and later. By default .NET 2.0 does not have TLS 1.2 support enabled.
To allow .NET 2.0 compiled applications to communicate using TLS 1.2 ensure the latest version of .NET 3.5.1 is installed on the system. Once confirmed, follow the steps outlined below to enable TLS 1.2 for .NET 2.0.
For more information on enabling strict usage of TLS 1.2 in Microsoft Exchange see the following Microsoft articles:
TLS 1.2 for .NET 2.0:
TLS/SSL Protocols by Windows OS:
Exchange strict usage of TLS 1.2 only.