Overview
This article provides information on why Kerio Control SPF is rejecting the emails incoming through the Spam Filter service provider and how you can resolve the issue.
Information
The problem is happening because you are using both an external Spam Filter Service provider and SPF check in Kerio Connect. The crux of the issue is that mail is being received from Spam Filter Server instead of the actual domain expected because of the way MX has been set up.
To resolve this, check if they perform SPF checks as part of their spam filtering process and proceed as suggested in Will enabling ‘do not check SPF IP addresses’ for Spam Filter Servers disable SPF Checking?