To allow the Cisco ESA to encrypt an email using the CRES (Cisco Registered Envelope Service), a provisioned email encryption profile must be configured on Cisco ESA. A provisioned email encryption profile is a type of encryption profile that specifies how messages are encrypted using CRES, such as the encryption key strength, the notification options, the branding settings, etc.
https://www.cisco.com/c/dam/en/us/products/collateral/security/esa-cres-encryption.pdf