Large amount of spool emails using the same domain as the sender’s email address are targeted to your domain despite enabling the SPF function in Kerio Connect.
Please check if the errors in the logs are for the same domain for which the SPF was added.
To reduce spoofing (and ensure that your own emails are delivered safely), please add an SPF record for all domains. Otherwise, you will still get spoof email coming through the filter for the specific domain that doesn't have an SPF record configured.
If this doesn’t solve your problem, please contact support with the error logs.