When reporting spam that slips past the filters, it is essential that we receive the full message headers from a message. Additionally, sometimes our Support department may request the full headers from an email message in order to troubleshoot mail delivery problems.
Every single Internet e-mail message is made up of two parts the header and the message body of the email. Every single email you send or receive on the Internet contains an Internet Header, a full and valid e-mail header provides a detailed log of the network path taken by the message between the mail sender and the mail receiver(s) (email servers).
Continue reading here https://mxtoolbox.com/Public/Content/EmailHeaders/
