The Insert X-Header action adds an X-Header to the message header before sending a message to the intended recipients. An X-Header consists of a name field and a body field, which can be customized according to your requirements.
Insert X-Header is one of the "Modify" class of actions.
Do not use or start your X-Header name (case-insensitive) with the following since they are reserved for Hosted Email Security:
The reserved X-Headers might be adjusted dynamically if necessary.