Reply-To :
The email address you send your response too.
From :
Displays the message sender; very easy to forge.
Content type :
Tells your browser or email client how to interpret the content of the email. Most common character sets are UTF-8 and ISO-8859-1.
MIME-Version :
Declares the email format standard in use. The MIME-Version is typically 1.0.
Subject :
The subject of the email contents.
To :
The intended recipients of the email; may show other addresses.
DKIM-Signature :
Domain Keys Identified Mail authenticates the domain the email was sent from and should protect against email spoofing and sender fraud.
Received :
The Received line lists each server that the email travels through before hitting your inbox. You read Received lines from bottom to top; the bottom-most line is the originator.
Authentication-Results :
Contains a record of the authentication checks carried out; can contain more than one authentication method.
Received-SPF :
The Sender Policy Framework (SPF) forms part of the email authentication process that stops sender address forgery.
Return-Path :
The location where non-send or bounce messages end up.
ARC-Authentication-Results :
The Authenticated Receive Chain is another authentication standard; ARC verifies the identities of the email intermediaries and servers that forward your message to its final destination.
ARC-Message-Signature :
The signature takes a snapshot of the message header information for validation; similar to DKIM.
ARC-Seal :
Seals the ARC authentication results and the message signature, verifying their contents; similar to DKIM.
X-Received :
Differs to Received in that it is considered non-standard; that is to say, it might not be a permanent address, such as a mail transfer agent or Gmail SMTP server.
X-Google-Smtp-Source :
Shows the email transferring using a Gmail SMTP server.
Delivered-To :
The final recipient of the email in this header.