According to the User Guide for Cisco Secure Email Encryption Service Add-In 1, the 'Use-Script' option allows you to use JavaScript in the encrypted message envelope. This option is enabled by default, but you can disable it if you want to send encrypted messages to recipients who have security policies that block JavaScript attachments[2, p. 14].
The other options are not valid because:
A) Inserting the X-PostX-Use-Script header with a value of false to the encrypted messages is not a supported feature of the Cisco Secure Email Encryption Service Add-in1.
B) Selecting JavaScript-free option within the Cisco Secure Email Encryption Service Add-in is not a valid option. The add-in does not have such an option1.
C) Creating an outgoing content filter and adding the Encrypt and Deliver Nov/ action with Use-Script option deselected is not possible. The Encrypt and Deliver Nov/ action does not have a Use-Script option[2, p. 13].