You can buy the S/MME certificate from a retailer or a Certificate Authority. If you are working in an organization, you can contact your IT Administrator for the same. The Certificate Authorities provide the S/MIME certificates as a PKCS #12 file. While downloading the PKCS #12 file, you have to create a strong password. Keep this file in a safe place as it contains the private key which is required to decrypt the emails. To send the encrypted emails using S/MIME, you have to install the S/MIME certificate in Outlook or another email client.