SMSMSE 6.x supports upgrades from Symantec Mail Security for Microsoft Exchange 4.6.x and higher. If you have version 4.5 or earlier you must uninstall that version and then install SMSMSE 6.x.
Note regarding Microsoft Cluster configurations If you are using a Microsoft Cluster, and have a Symantec Mail Security cluster resource, you must delete the cluster resource and uninstall Symantec Mail Security before installing a newer version or build.
It is recommended that you back up the existing configuration files prior to upgrading. The backup files are for use in the case of a failed migration to ensure that you can easily roll back to the previous version.