Are you asking what X-Headers Symantec Mail Security uses?  Or is there a specific item in the documentation that mentions X-Headers that needs clarification?

Hi,

When a message is initially generated it should include standard headers such as From:, To:, Subject:, Date:, Message-ID. Other standard headers include Received:, Cc:, Bcc:, etc.

In general X-header can refer to any non-standard header added during the sending of an email. X-headers can be added at any stage. Some examples of X-headers are:
X-Mailer:
X-Spam-Reason:
X-Brightmail-Tracker:

Hope that helps!

Amanda

The Xheader contains the information needed to deliver the message to the spam
folder instead of to the inbox.

To use this feature, you must deploy the optional plug-in for Microsoft Outlook
to the desktop computers on your network. The plug-in is available on the
Symantec Mail Security for SMTP installation CD.

Mark for Spam Folder

You must have the Agent installed on the Exchange or Domino server through which you are routing mail for this
to function. An X-header will be added to allow the Agent to move the message to the user’s spam folder. It will display as
X-bmifolder:1.

You cannot modify this X-header.