The additional "X-Source" headers are optional and configurable via WHM at the following menu path:
WHM:
Main >>
Server Configuration >>
Tweak Settings >>
Mail- "Track the origin of messages sent though the mail server by adding the X-Source headers (exim 4.34+ required)"
The additional headers are for informational purposes only. Please be aware it is best to keep them enabled so that when there is real Spam sent from your system then your Systems Administration team can have the added information available when attempting to investigate and track which account abused resources to send Spam. If the option is disabled that will make it increasingly difficult to investigate Spam issues; if Spam is repeatedly sent and recurs without stopping it will ultimately result in your server's being permanently blacklisted.