If you want to export Kerio Mailbox to PST, then use Kerio Converter. It import entire Kerio emails to Outlook PST along with contacts, calendars, notes, attachments and other information. This utility is comaptible with all the versions of MS Outlook. 

Key Features of Kerio Converter

• Convert Kerio emails to PST file
• Export Kerio contacts to vCard format
• Hold all the key elements of emails
• Preserves the folder strcture during conversion
• Gurauntee of complete migration