Overview

The customer is experiencing issues with connecting to the Kerio Connect server. The problem seems to be related to authentication, specifically with Secure Sockets Layer (SSL) and Transport Layer Security (TLS) during the handshake process. The customer suspects that a recent Microsoft or Kerio Offline Connector (KOFF) update may have introduced a TLS issue. Despite various troubleshooting steps, the issue persists. The problem does not occur on a new system with Windows 11 and Office 2019.

Solution

The issue was resolved by adding a missing registry key on the client's machine. The following steps were taken:

1. Open the Windows Registry Editor.
2. Navigate to the following path: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0
3. Add the following keys and values:
   • "Auth132" with the value "IISSUBA"
   • "NtlmMinClientSec" with the value dword:20000000
   • "NtlmMinServerSec" with the value dword:20000000

After adding these registry keys, the authentication issue with the Kerio Connect server was resolved.

Summary

Authentication issues with the Kerio Connect server, specifically related to SSL and TLS during the handshake process, can be resolved by adding specific registry keys on the client's machine.