Email Headers
A header is most basically all of the information contained in an email other than the body and any attachments. This data is separated into a number of different fields that appear at the top of the message. In everyday usage a recipient will normally not see all of the fields that make up a header. The information contained in a header is vital for making sure that the email is delivered successfully to the intended recipient. Header fields include:
From - This field includes the email address from which the message was sent. The name of the sender can also be found here if the sender has this option selected in their email configuration options.
To - The “to” field will contain the email address or addresses of the recipients designated by the sender. It may also contain the names of the recipients if that information was entered in the sender’s address book.
Subject - A brief description of what the body of the message contains.
Date - This field is made up of the date and time when the email was composed and sent.
CC - Short for “Carbon Copy” or “Courtesy Copy” this field is used to include additional recipients of secondary importance. Recipients specified in the “CC” field are being apprised of the message only and are not expected to have to reply. Those listed in the ‘To” field will be able to see those listed in the “CC” field.
BCC - “BCC” is an abbreviation of “Blind Carbon/ Courtesy Copy.” Recipients listed in the ‘BCC” field will not be able to see the addresses and/ or names of any of the other recipients of the email (including others in the “BCC” field).
Received - Data that has been collected and appended to the message by mail servers that have handled or forwarded a message before the recipient received it.
Content-Type - Instructions as to how the message must be displayed, whether plain text, HTML, etc.
Reply-To - This section lists the address that should be used in any reply to the original sender.
References/ In-Reply-To - This refers to both the identification of the email to which the current reply is addressed as well as the ID of the current message.
Most email programs have a feature for configuring how much of this information that you want to see when receiving a message. Knowing one’s way around all the various parts of a header can help spot things such as spam and spoofed email addresses. Inconsistencies in the various fields above can often point to an email originating from a questionable source.