SMTP is not transported over TLS 1.1 or TLS 1.2 protocol in an Exchange Server 2013 environment Content provided by Microsoft Applies to: Exchange Server 2013 EnterpriseExchange Server 2013 Standard Edition Select Product Version All Products Symptoms Simple mail transfer protocol (SMTP) uses transport layer security (TLS) 1.0 in a Microsoft Exchange Server 2013 environment, even if you have enabled TLS 1.1 or TLS 1.2. 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 cumulative update:Cumulative Update 8 for Exchange Server 2013Note 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. Last Updated: Mar 17, 2015 Did this solve your problem? Yes No Tell us what we can do to improve the article Submit Thanks! Your feedback will help us improve the support experience.