SMTP is not transported over TLS 1.1 or TLS 1.2 protocol in an Exchange Server 2010 environment

Symptoms

If you enable transport layer security (TLS) 1.1 or TLS 1.2 in a Microsoft Exchange Server 2010 environment, simple mail transfer protocol (SMTP) uses TLS 1.0 unexpectedly.

Cause

This issue occurs because of a hard-coded restriction that limits SMTP to use secure sockets layer (SSL) 3.0 and TLS 1.0 for transport.

Resolution

To resolve this issue, install the following update:

Update Rollup 9 for Exchange Server 2010 Service Pack 3
Note This update removes the hard-coded restriction so that SMTP sessions can negotiate with any SSL or TLS protocols that are enabled in the host operating system.

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about TLS and SSL protocols, see What is TLS/SSL.
For more information about how to enable TLS 1.2 protocol in registry key, see TLS/SSL Settings.

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