In order for us to troubleshoot email issues or to investigate phishing emails source IP, we need the actual email as an attachment to examine the source header. In order to do that, u need to forward the email "as an attachment" U can follow the links below to do that.
https://www.greennet.org.uk/support/how-forward-email-attachment
https://sg.godaddy.com/help/outlook-2013-forward-email-messages-as-attachments-4822