“Microsoft Windows update breaks Microsoft Outlook connectivity with Kerio Connect mail server”
We have discovered email sending issues with certain Microsoft Windows users who use Microsoft Outlook email client and Kerio Connect mail server. The symptoms are that Outlook cannot send email.
The problem is caused by a recent Windows Security Update that makes changes to TLS (SSL) secured connections used by the KOC (Kerio Offline Connector) plugin for Outlook.
The resolution here is to update your Kerio Connect server to version 7.3.1 patch 2. When you upgrade your Kerio Connect server you will also need to update KOC plugin used by Outlook on Windows workstations. The update is relatively painless in that it should auto-update the KOC plugin the next time the user opens Outlook.
More detailed information on this update can be found here.
Big thank you to Vicky at Kerio Inc for bringing this to our attention.