You are facing an issue that a Blacklist entry is not found in the List by Blacklist provider, but still exists in Kerio logs as blocked. You are getting an error message in the log as below:
IP address <ipaddress> found in DNS blacklist <Blacklist Provider>, mail from <senderemail> to <receiveremail> rejected
The result is not generated by Kerio Connect, but is sent by the Blacklist provider.
If a legitimate IP is listed, please contact the Blacklist provider directly to understand why.
We can't control which IPs they list or not. However, you can customize its behavior as detailed in Spam Blacklist function is blocking legitimate emails from external users article.