About the Mail Security license serial number
Your license certificate or upgrade voucher, which contains the license number, arrives within three to five business days of when you receive your software. Contact Symantec Customer Service at 800-721-3934 or your reseller to check the status of your order if you do not receive the license certificate or upgrade voucher. Contact Symantec License Administration if you have lost your license certificate or upgrade voucher.
You may not be able to install the license if you are using the console on the Windows Server 2019 Core installation. You can use the remote console to install the license.