The email header is a code snippet in an HTML email, that contains information about the sender, recipient, email's route to get to the inbox and various authentication details. The email header always precedes the email body.
Finding the Email Headers
Refer to this article called How to Get Email Headers from the MXToolbox website to find the email headers for various email clients and webmail providers. Email headers can provide valuable diagnostic information like hop delays, anti-spam results and more.
Analyzing the Email Headers
Once the email header is obtained, you can use one of the following Email Header Analyzer tool.