Symantec issues a serial number when you purchase Mail Security. If you want to upgrade from a previous version of the product and you have an active maintenance contract, Symantec issues an upgrade voucher with an alpha-numeric code. Register the serial number or upgrade code to receive a license key for the associated license file.
License keys are delivered in a Symantec license file (.slf). The serial number is provided on a license certificate, which is mailed separately and arrives in the same time frame as your software. For security reasons, the license certificate is not included in the Mail Security software distribution.
See About renewing the Mail Security license
License activation involves the following process: