Ideally, if you find a conflict in Norton which prevents SMTP or POP3 delivery of Kerio emails, you should contact Symantec and get them to fix the bug in their product. Most customers do not make this effort. Instead, they simply want to uninstall their Norton.
Some versions of Norton do not uninstall correctly using the add/remove programs dialog. They break it such that it cannot re-installed again at a later date.
Symantec has a knowledge base article about how to completely remove their products. Here is a link to the document: Removing your Norton program using SymNRT
Beware of one more thing. Sometimes, Norton can leave a dependency in your DHCP client service. This will cause workstations to fail getting an IP address from DHCP. Check the registry for HKLM\SYSTEM\ControlSet001\Services\Dhcp\DependOnService and open it up. If there is a service called SymTDI, remove it.