I'm unable to get the token FILE to work as documented:

${FILE, path} - Includes the content of a specified file.
path - The path to the file. Relative to the workspace root.

In the mail content definition I have something like

Executed with the following <b>build.cs</b>:<br/>
${FILE,build.cs}

In the mail received it just shows the normal html result but without evaluating the token FILE and including the content of the file build.cs (which is visible on the root of workspace).