An email header precedes the body of an email and includes detailed and often technical information about when and from where the email was sent. This includes at least the sender's email address, the recipient's email address, and the subject and date of the email. Further information such as CC is also possible if additional recipients have been entered for the email.
An email header also contains the mail server and the IP address of the sender.
Depending on the sending mail server's settings, a header may contain additional information.