The configuration that is needed to accomplish the goal of adding protection for data in transit and having headers in the email message is to deploy an encryption appliance. An encryption appliance is a device that encrypts and decrypts email messages using various encryption standards, such as S/MIME, PGP, or Cisco Registered Envelope Service (CRES). An encryption appliance can also add headers to the email message to indicate the encryption status, the encryption key, or the encryption policy. An encryption appliance can be integrated with an email appliance, such as Cisco Email Security Appliance (ESA), to provide end-to-end email security and encryption.
The other options are incorrect because:
* Provisioning the email appliance is not enough to add protection for data in transit and have headers in the email message. An email appliance can provide various email security features, such as spam filtering, virus scanning, content filtering, or data loss prevention, but it does not encrypt or decrypt email messages by itself. An email appliance needs to work with an encryption appliance to provide email encryption and decryption.
* Mapping sender IP addresses to a host interface is not related to adding protection for data in transit and having headers in the email message. This is a configuration option for an email appliance that allows it to accept email messages from specific IP addresses or ranges and assign them to a specific host interface. This can be useful for load balancing, traffic management, or policy enforcement, but it does not affect email encryption or decryption.
* Enabling flagged message handling is not relevant to adding protection for data in transit and having headers in the email message. This is a configuration option for an email appliance that allows it to handle email messages that have a specific flag or tag in the subject line or the body. This can be useful
* for testing, troubleshooting, or applying special policies, but it does not affect email encryption or decryption.
References:
* Cisco Email Encryption
* Cisco Email Encryption Appliance
* Cisco Email Security Appliance Configuration Guide