To improve the security of connections to Citrix Listener Service used for Secure Mail notifications, Citrix will block any communication over Transport Layer Security (TLS) 1.0 and 1.1 as of August 31st, 2020.

Affected Component: Push Notifications for Secure Mail.

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Instructions

All connections from on-premises Exchange Server and Proxy server will need to be able to communicate with the Citrix Listener Service over TLS 1.2 as of August 10th, 2020.

In order to verify the TLS communication on Microsoft Exchange Server, Please capture the Network traces using Wireshark.
Verify the protocol and the version used in client hello

 
To Enable TLS 1.2 on Microsoft Exchange servers please follow steps mentioned in the guides below

• Patches and updates required for TLS 1.2 on Exchange and Windows: https://techcommunity.microsoft.com/t5/exchange-team-blog/exchange-server-tls-guidance-part-1-getting-ready-for-tls-1-2/ba-p/607649
• Enabling TLS 1.2 protocol on Exchange and Windows: https://techcommunity.microsoft.com/t5/exchange-team-blog/exchange-server-tls-guidance-part-2-enabling-tls-1-2-and/ba-p/607761